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A Library  of 
Universal  Literature 

IN  FOUR  FARTS 

Comprising  Science,  Biography,  Fiction 
and  the  Great  Orations 

FART  ONF— SCIENCE 


ELECTRICITY  IN 
MODERN  LIFE 

By  G.  W.  DE  TUNZELMANN,  B.Sc. 


NEW  YORK 

P.  F.  COLLIER  AND  SON 

• M C M • 

13 


PRESS  OF 

P.  F.  COLLIER  & SON 


ALL  RIGHTS  RESERVED 


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5 31.^  remote  ^ 

T^5e.. 

13^0  BOARD  OF  EDITORS 
SCIENCE 

ANGELO  HEILPRIN,  author  of  ^‘The  Earth  and  Its  Story,” 
etc. ; Curator  Academy  of  Natural  Sciences  of 
Philadelphia. 

JOSEPH  TORREY,  JR.,  Ph.D.,  Instructor  in  Chemistry  in 
Harvard  University. 

RAY  STANNARD  BAKER,  A.B.,  author  of  “The  New  Pros- 
perity,” etc.;  Associate  Editor  of  McClure’s  Magazine. 


BIOGRAPHY 


MAYO  W.  HAZELTINE.  A.M.,  author  of  “Chats  About 
Books,”  etc.;  Literary  Editor  of  the'  New  York  Sun. 
JULIAN  HAWTHORNE,  author  of  “Nathaniel  Hawthorne  and 
His  Wife,”  “History  of  the  United  States,”  etc. 
CHARLES  G.  D.  ROBERTS,  A.B.,  A.M.,  author  of  “A 
History  of  Canada”;  late  Professor  of  English  and 
French  Literature,  King’s  College. 


FICTION 


RICHARD  HENRY  STODDARD,  author  of  “The  King’s 
Bell,”  etc.,  etc.;  Literary  Editor  of  the  New  York 
Mail  and  Express. 

^ HENRY  VAN  DYKE,  D.D.,  LL.D.,  author  of  “Little  Rivers,” 

^ etc.,  etc.;  Professor  of  English  Literature  at  Princeton 

' University. 

THOMAS  NELSON  PAGE,  LL.D.,  Litt.D.,  author  ot  “Red 
Rock,”  etc.,  etc. 

ORATIONS 

■3 

HON.  HENRY  CABOT  LODGE,  A.B.,  LL.B.,  author  of 
“Life  of  Daniel  Webster,”  etc.;  U.  S.  Senator  from 
Massachusetts. 

HON.  JOHN  R.  PROCTOR,  President  U.  S.  Civil  Service 
Commission. 

MORRIS  HICKEY  MORGAN,  Ph.D.,  LL.D.,  Professor  in 
Latin,  Harvard  Universitv.  * 

* V \ 

939 1 00 


A LIBRARY  OF 
UNIVERSAL  LITERATURE 

SCIENCE 

Volume  Thirteen 


CONTENTS 


CHAPTER  I 

WHAT  WE  KNOW  ABOUT  ELECTRICITY 7 

CHAPTER  II 

WHAT  WE  KNOW  ABOUT  MAGNETISM 20 

CHAPTER  III 

MUTUAL  ACTIONS  BETWEEN  MAGNETS  AND  CONDUCTORS  TRAVERSED  BY 


ELECTRIC  CURRENTS 2t 

CHAPTER  lY 

FORCE,  WORK,  AND  POWER 32 

CHAPTER  Y 

SOURCES  OP  ELECTRICITY 41 

CHAPTER  YI 

MAGNETIC  FIELDS 56 

CHAPTER  YII 

ELECTRICAL  MEASUREMENT 69 

CHAPTER  YIII 

MAGNETO  AND  DYNAMO  ELECTRIC  MACHINES 19 

CHAPTER  IX 

THE  STORY  OP  THE  TELEGRAPH  . . * 94 

CHAPTER  X 

OVERLAND  TELEGRAPHS . . .121 

CHAPTER  XI 


SUBMARINE  TELEGRAPHS  . . - . . . . . . .150 

(3) 


4 


CONTENTS 


CHAPTER  XII 

THE  TELEPHONE 169 

CHAPTER  XIII 

THE  TELEPHONE  EXCHANGE  SYSTEM 200 

CHAPTER  XIY 

DISTRIBUTION  AND  STORAGE  OF  ELECTRICAL  ENERGY  . . • . 208 

CHAPTER  XV 

ELECTRIC  LIGHTING 221 

CHAPTER  XVI 

ELECTRO-MOTORS  AND  THEIR  USES 246 

CHAPTER  XVII 

ELECTRO-METALLURGY • . . 257 

CHAPTER  XVIII 

ELECTRICITY  IN  WARFARE 266 

CHAPTER  XIX 

MEDICAL  ELECTRICITY , , .2'75 

CHAPTER  XX 

MISCELLANEOUS  APPLICATIONS  OF  ELECTRICITY 281 

» 


ELECTRICITY  IN  MODERN  LIFE 


PREFACE 


In  this  little  volume  I have  endeavored  to  give  a brief 
but  intelligible  and  connected  sketch  of  the  more  important 
of  the  numerous  useful  functions  fulfilled  by  Electricity  in 
modern  daily  life,  the  scientific  principles  underlying  these 
practical  applications,  and  the  history  of  their  development. 

It  is  addressed  primarily  to  readers  who  have  no  previous 
knowledge  of  the  subject,  but  who  wish  to  know  something 
of  what  Electricity  has  been  made  to  do  for  us,  and  of  how 
it  has  been  made  to  do  it.  I trust,  however,  that  it  may  also 
be  of  some  use  to  students  who  are  just  beginning  the  study 
of  practical  Electricity,  by  giving  them  a general  view  of  the 
field  of  knowledge  which  they  will  afterward  have  to  study 
in  detail. 

I have  to  thank  my  friend.  Professor  Sylvan  us  P.  Thomp- 
son, and  his  publishers,  Messrs.  Spon,  for  permission  to  use 
his  excellent  series  of  skeleton  diagrams  illustrating  the 
principles  of  dynamo  construction  and  regulation,  together 
with  some  other  illustrations  from  his  “Dynamo-Electric 
Machinery,”  a most  valuable  work,  which  every  electrical 
engineering  student  should  not  only  obtain,  but  carefully 
study.  I am  also  indebted  to  Professor  Thompson  and  his 
publishers  for  the  illustrations  of  Reis’s  Telephone,  which 
are  taken  from  his  book  on  the  subject. 

My  friend,  Mr.  Preece,  and  his  publishers,  Messrs.  Long- 
mans, and  Messrs.  Whitaker,  have  laid  me  under  great 
obligations  by  their  permission  to  make  free  use  of  the 

(5) 


6 


PREFACE 


illustrations  in  Preece  and  Sivewright’s  standard  work  on 
Telegraphy,  and  in  Preece  and  Maier's  recently  published 
volume  on  the  Telephone. 

1 also  have  to  express  my  thanks  to  the  editors  and  pub- 
lishers of  “The  Electrician”  and  “Engineering”  for  the  use 
of  illustrations,  and  to  Messrs.  Crosby,  Lockwood  & Co.  for 
some  illustrations  which  I have  taken  from  Sabine’s  valuable 
historical  work  on  the  Electric  Telegraph. 

In  tracing  the  history  of  the  telegraph  and  of  submarine 
telegraphy  I have  been  much  indebted  to  Mr.  J.  J.  Fahie’s 
“History  of  Electric  Telegraphy,”  which  first  appeared  in 
the  pages  of  “The  Electrician,”  and  to  Wiinschendorfi’s 
“Traite  de  Telegraphic  Sous-Marine,”  the  best  work  on 
Submarine  Telegraphy  which  has  yet  been  published. 
Lastly,  I have  to  thank  my  brother,  E.  W.  de  Tunzelmann, 
M.B.,  for  contributing  the  chapter  on  Medical  Electricity. 

G.  W.  He  Tunzelmann. 

66  Longridge  Road, 

South  Kensington, 

October  30,  1889. 


ELECTRICITY  IN  MODERN  LIFE 


CHAPTER  I 

WHAT  WE  KNOW  ABOUT  ELECTRICITY 

IT  WOULD  be  of  the  greatest  interest  to  trace  the  progress 
of  our  knowledge  of  electrical  phenomena  from  the  early 
time  when  the  Greek  philosopher  Thales  first  observed 
that  a piece  of  amber  rubbed  with  various  substances  was 
capable  of  attracting  light  objects,  but  the  story  would  de- 
mand a volume  to  itself.  I will  try,  therefore,  to  set  forth, 
as  briefly  as  possible,  the  present  state  of  our  knowledge 
of  the  nature  of  electrical  phenomena  and  of  the  means  by 
which  electrical  actions  may  be  produced. 

If  a dry  glass  rod  is  rubbed  with  one  of  sealing-wax  or 
resin,  and  the  rods  are  hung  up  by  threads  so  that  they  can 
move  freely,  they  will  be  found  to  attract  each  other;  but  if 
two  rods  of  resin^mbbed  with  glass,  or  of  glass  rubbed  with 
resin,  are  hung  dp  near  together  they  will  repel  each  other. 

The  rods  are  then  said  to  be  electrified,  and  as  they 
exhibit  two  distinct  phenomena — namely,  attraction  and 
repulsion — we  see  that  there  are  two  distinct  kinds  of 
electrification. 

If  the  rods  are  laid  aside  for  a short  time  they  will  be 
found  to  have  lost  their  power  of  attracting  or  repelling 
each  other.  These  phenomena  may  be  shown  still  more 

(7) 


8 


ELECTRICITY  IN  MODERN  LIFE 


clearly  by  rubbing  the  rods  with  silk,  when  it  will  be  found 
that  two  similarly  rubbed  rods  will  repel  each  other  and  two 
dissimilarly  rubbed  rods  will  attract  each  other.  The  elec- 
trification of  glass  rubbed  with  silk  is  known  as  vitreous 
electrification,  and  that  of  resin  rubbed  with'  silk  as  resin- 
ous electrification. 

The  ordinary  cylinder  or  plate  electrical  machines  are 
simply  convenient  devices  for  rubbing  a glass  plate  or  cylin- 
der with  silk  or  other  suitable  substance  in  such  a manner 
as  to  obtain  electrification  in  a comparatively  large  quantity. 
The  electricity,  as  it  is  obtained  from  such  a machine,  is 
allowed  to  pass  to  a cylinder  of  brass  supported  upon  glass 
legs,  usually  known  as  the  prime  conductor,  and  after  the 
machine  has  been  in  action  for  a short  time,  it  will  be  found 
that  on  bringing  the  finger  to  the  prime  conductor  a spark 
will  pass.  If  before  trying  this  experiment  the  prime  con- 
ductor is  connected  with  the  ground  by  a wire  or  chain,  no 
spark  will  be  obtained.  The  reason  for  this  is  that  the  elec- 
trification produced  upon  the  prime  conductor  is  not  able  to 
pass  through  the  glass,  but  passes  away  as  rapidly  as  it  was 
produced  through  the  wire  or  chain.  This  shows  that  some 
substances  will  allow  electricity  to  pass  through  them  with 
facility;  such  substances  are  called  good  conductors.  Other 
substances  only  allow  electricity  to  pass  with  great  difficulty, 
and  they  are  called  bad  conductors  or  insulators.  The  best 
conductors  known  are  metallic  bodies. 

Dry  silk  is  a bad  conductor  of  electricity,  and  therefore 
a conductor  suspended  by  a dry  silk  thread  will  retain  its 
electrification  for  a considerable  time.  Resin,  and  glass  free 
from  lead,  are  even  worse  conductors,  or,  in  other  words, 
better  insulators  than  silk,  and  are  therefore  commonly  used 
in  making  insulating  stands  for  electrical  apparatus.  They 


WHAT  WE  KNOW  ABOUT  ELECTRICITY 


9 


must  be  kept  dry,  for  if  a film  of  moisture  is  allowed  to  form 
upon  their  surfaces  this  film  will  carry  away  the  electrifica- 
tion. Air  and  other  gases  are  absolutely  perfect  insulators. 
A simple  and  convenient  instrument  for  detecting  electri- 
fication consists  of  a small  pith-ball  suspended  from  a sup- 
port by  means  of  a dry  silk  thread.  If  an  electrified  body 
is  brought  near  to  such  a ball  it  will  attract  it,  but  when  it 
comes  into  contact  with  the  charged  body  the  ball  will  take 
a portion  of  its  charge  and  will  be  immediately  repelled. 
Such  an  instrument,  being  capable  of  indicating  the  exist- 
ence of  electrification,  is  called  an  electroscope. 

Take  a rod  of  resin  or  sealing-wax,  and  have  a small 
flannel  cap  made  to  fit  exactly  over  the  end  of  the  rod,  and 
having  attached  to  it  a dry  silk  thread.  Now  place  the  cap 
upon  the  end  of  the  rod  and  turn  it  round  several  times  so 
as  to  rub  it  against  the  rod,  and  then  bring  the  rod  and  the 
cap  together  to  the  suspended  pith-ball — it  will  have  no  effect 
whatever  upon  the  ball;  but  if  the  flannel  cap  is  removed  by 
means  of  the  silk  thread  and  brought  near  to  the  pith-ball 
it  will  attract  the  ball  just  as  the  charged  conductor  did, 
and  after  the  ball  has  touched  the  flannel  it  will  be  repelled. 
If  the  rod  which  was  rubbed  with  the  flannel  is  then  held 
near  the  pith-ball,  the  ball  which  was  before  repelled  will 
be  attracted. 

Now  I will  suppose  that  the  reader  has  no  further  knowl- 
edge of  what  electrification  consists  in  than  has  been  fur- 
nished by  the  foregoing  experiments,  and  I will  ask  him 
to  consider  what  information  they  can  give  concerning  its 
nature.  What  has  been  proved  is  that  no  electricity  is  act- 
ually generated,  for  the  electrifications  of  the  two  bodies 
are  equal  in  amount,  but  opposite  in  sign. 

Imagine  for  a moment  that  electrifying  a body  positively 


10 


ELECTRICITY  IN  MODERN  LIFE 


consists  in  adding  a certain  something  to  it,  then  electrifying 
it  negatively  to  the  same  extent  will  simply  mean  taking 
away  an  equal  amount  of  that  something  from  it.  At  this 
stage  an  analogy  will  be  of  assistance,  for  the  great  difficulty 
of  forming  exact  conceptions  of  electrical  action  lies  in  the 
fact  that  we  have  no  electrical  sense.  We  are  able,  by  means 
of  our  ordinary  senses,  to  detect  the  presence,  or  the  trans- 
ference from  one  place  to  another,  of  solids,  liquids,  or 
gases.  Our  senses  again  will  tell  us  when  one  body  is  hot- 
ter than  another;  but  we  have  no  corresponding  means  of 
directly  determining  whether  one  conductor  is  more  or  less 
highly  charged  with  electricity  than  another.  Consider, 
then,  what  happens  when  a liquid — such  as  water,  for  ex- 
ample— is  poured  from  one  vessel  into  another.  If  we  have 
a certain  quantity  of  water  contained  in  two  vessels,  we  may 
pour  water  from  one  into  the  other;  but  the  exact  amount 
poured  into  one  must  be  taken  out  of  the  other,  always  sup- 
posing that  no  water  is  brought  in  from  outside,  and  that 
no  loss  takes  place  of  the  total  amount  in  the  two  vessels. 

Now  carry  the  analogy  a step  further.  Suppose  the  water 
to  be  at  the  same  level  in  the  two  vessels,  and  suppose  we 
have  the  means  of  connecting  the  two  by  a tube,  by  which 
water  can  be  driven  from  one  into  the  other.  To  do  this, 
suppose  the  vessels  to  be  cylinders,  and  suppose  that  a pis- 
ton fits  air-tight  into  each  cylinder,  and  floats  upon  the  water 
contained  in  it.  Imagine  that  the  vessels  are  opaque,  so  that 
we  cannot  see  what  goes  on  inside  them;  but  assume  that  we 
have  the  means  of  forcing  down  one  of  the  pistons,  so  as  to 
drive  the  water  into  the  other  vessel.  Let  the  space  above 
the  piston  in  each  cylinder  be  occupied  by  air,  and  let  a tube 
with  a narrow  opening  be  fitted  into  the  top  of  each  cylin- 
der. Now  let  the  pair  of  cylinders  be  given  to  some  one 


WHAT  WE  KNOW  ABOUT  ELECTRICITY 


11 


who  is  ignorant  of  what  they  contain,  and  ask  him  to  work 
the  mechanism  for  depressing  the  piston.  Suppose,  more- 
over, that  he  does  not  know  which  piston  is  depressed  by 
the  mechanism.  He  will  have  no  direct  means  of  observing 
the  amount  of  water  inside;  but  if  he  allows  some  light  ob- 
jects, such  as  pieces  of  tissue  paper,  to  fall  near  the  ends 
of  the  two  projecting  tubes,  he  will  find  that  the  paper  is 
attracted  toward  one  tube  and  repelled  from  the  other — the 
reason,  of  which  he  knows  nothing,  being  that  the  water, 
which  is  forced  into  one  cylinder,  drives  out  the  air  above 
it  through  its  tube,  while  the  descent  of  the  piston  in  the 
other  cylinder  allows  air  to  rush  in  through  its  tube.  He 
‘will  therefore  find  two  different  effects  produced — namely, 
attraction  of  the  paper  to  one  tube,  and  its  repulsion  from 
the  other.  If  now  he  takes  a tube  of  the  form  of  the  letter 
“Y,”  and  connects  the  two  arms  by  means  of  India-rubber 
tubes  with  the  tubes  issuing  from  the  two  cylinders,  he  will 
find  that  pieces  of  paper  placed  near  the  stem  of  the  “Y’’ 
tube  will  neither  be  attracted  nor  repelled,  the  reason  of 
course  being  that  the  amount  of  air  sucked  into  one  cylinder 
is  equal  to  the  amount  driven  out  of  the  other,  so  that  no  air 
is  either  driven  out  of  the  stem  of  the  “Y’’  tube  or  sucked 
into  it.  We  must  suppose  that  the  experimenter  is  only 
able  to  observe  the  attraction  of  the  paper  to  one  tube  and 
its  repulsion  from  the  other,  and  that  he  has  no  means  of 
finding  out  that  these  are  caused  by  the  expulsion  of  the  air 
from  one  tube  and  by  its  being  sucked  into  the  other.  He 
will  therefore  have  exactly  similar  data  to  those  obtained 
from  the  electrical  experiments,  and  he  will  draw  the  con- 
clusion that  the  effect  of  working  the  mechanism  is  to  cause 
the  two  cylinders  to  give  rise  to  two  distinct  effects,  but 
that  the  sum  total  of  the  two  actions  is  zero.  This  analogy 


12 


ELECTRICITY  IN  MODERN  LIFE 


will  help  to  explain  how  it  is  that  though  we  know  abso- 
lutely nothing  of  what  electricity  really  is,  yet  we  are  en- 
titled to  assert  that,  when  electrification  takes  place,  some- 
thing occurs  like  the  transference  of  an  incompressible  liquid 
from  one  place  to  another. 

In  the  application  of  electricity  to  practical  purposes  what 
is  required  is  either  to  maintain  a continuous  flow  of  electric- 
ity through  a conductor,  or  to  make  it  surge  repeatedly  back- 
ward and  forward  through  the  conductor.  It  is  therefore 
necessary  to  consider  the  means  by  which  electricity  can  be 
set  in  motion.  Take  a metallic  cylinder  resting  horizontally 
upon  an  insulating  stand,  and  from  each  end  of  it  suspend 
by  means  of  a thread  a pair  of  pith-balls.  Then  bring  one 
end  of  the  cylinder  near  to  a conductor  charged  with,  say, 
positive  electricity,  and  it  will  be  found  that  the  pith-balls 
will  immediately  diverge  from  each  other.  Now  rub  a piece 
of  sealing-wax  with  some  silk,  and,  keeping  the  charged 
conductor  near  the  end  of  the  insulated  cylinder,  bring  the 
sealing-wax  near  to  each  pair  of  balls  in  succession,  when  it 
will  be  found  that  the  pair  nearest  to  the  conductor  will  be 
repelled  from  it,  showing  that  the  nearer  end  of  the  cylinder 
with  the  balls  suspended  from  it  are  negatively  electrified. 
The  pair  at  the  other  end  of  the  cylinder  will  be  found  to 
be  attracted,  showing  that  the  further  end  is  positively 
electrified.  The  effect  of  bringing  the  insulated  cylinder 
near  to  the  positively  charged  conductor  has,  therefore, 
been  to  charge  its  further  extremity  positively  and  its  nearer 
extremity  negatively,  so  that  a positively  charged  body  not 
only  repels  a similarly  charged  body,  but  it  also  drives  elec- 
tricity, of  a similar  kind,  to  the  further  portion  of  the  con- 
ductor into  the  neighborhood  of  which  it  is  brought.  This 
is  called  electrical  induction. 


WHAT  WE  KNOW  ABOUT  ELECTRICITY 


13 


Consider  the  question  of  electrical  induction  somewhat 
further.  Take  a cylindrical  glass  jar,  and  coat  it,  both  in- 
side and  outside,  to  within  two  or  three  inches  of  the  top 
with  tin-foil.  Then  place  the  jar  upon  an  insulating  stand, 
and  connect,  by  means  of  a wire  or  chain,  one  of  the  tin-foil 
coatings — say,  the  inner  one — with  the  conductor  of  an  elec- 
trical machine,  and  work  the  machine  for  a short  time.  We 
should  then  expect  the  coating  in  connection  with  the  con- 
ductor of  the  machine  to  have  received  a charge  from  the 
latter.  If  the  jar  is  disconnected  from  the  conductor  we 
should  therefore  expect,  on  presenting  a finger  to  the  inside 
coating,  to  receive  a spark.  If  the  jar  is  thoroughly  dry  at 
the  time  of  making  the  experiment,  so  that  the  inner  coating 
is  well  insulated,  a small  spark  will  be  obtained  if  the 
machine  was  acting  properly;  but  it  will  be  a very  feeble 
one.  Now  repeat  the  same  experiment,  having  previously 
connected  the  outer  coating  with  the  earth.  It  will  then  be 
found  that  after  turning  the  machine  as  many  times  as  before 
a very  much  stronger  spark  will  be  obtained  on  presenting  a 
finger  -to  the  inner  coating,  thereby  connecting  it,  through 
the  observer’s  body  and  the  earth,  with  the  outer  coating; 
and  indeed,  if  the  jar  is  a large  one,  and  the  machine  is 
in  good  condition,  the  strength  of  the  spark  will  probably 
be  such  as  to  prevent  any  desire  for  a repetition  of  the 
experiment. 

Now,  what  is  it  that  has  taken  place,  and  what  is  the 
cause  of  the  difl'erence  in  the  two  cases  ? The  fluid  analogy 
will  here  again  be  of  assistance.  A conductor  will  be  repre- 
sented by  a tube;  and  an  insulator,  or,  as  Faraday  called  it, 
a dielectric,  by  a partition  across  the  tube,  which  will  not 
allow  water  to  flow  through  it,  but  of  such  a nature,  how- 
ever, that  the  water  upon  one  side  of  the  division  may  be. 


14 


ELECTRICITY  IN  MODERN  LIFE 


capable  of  acting  upon  the  water  at  the  other  side.  The 
latter  condition  is  necessary  in  order  to  represent  the  electri- 
cal actions,  for  it  has  been  pointed  out  that  when  a charged 
body  is  brought  near  to  a conductor,  but  is  separated  from 
it  by  a dielectric,  such  as  air,  for  example,  the  electricity 
similar  to  that  on  the  charged  body  is  driven  to  the  further 
portion  of  the  conductor. 

Suppose,  therefore,  that  the  tin-foil  coatings  of  the  jars 
are  represented  by  two  tubes,  while  the  dielectric,  glass,  is 
represented  by  a division,  consisting  of  a sheet  of  some  elas- 
tic substance — for  example,  a thin  sheet  of  India-rubber. 
The  opposed  surfaces  of  the  tin-foil  coatings  are  separated 
by  means  of  the  glass  of  the  jar,  and  one  of  the  non-opposed 
surfaces  is  in  contact  with  the  dielectric,  air,  while  the  other 
is  connected  with  the  conductor  of  the  electrical  machine. 
The  state  of  things  in  the  first  experiment  may  therefore  be 
represented  by  closing  up  the  end  of  one  of  the  tubes  with 
a second  sheet  of  India-rubber,  attaching  a pump  to  the 
other  tube  and  forcing  water  into  it.  The  India-rubber 
separating  the  two  tubes,  and  that  which  closes  the ‘end  of 
the  tube  furthest  from  the  pump,  will  stretch  slightly,  and 
therefore  a small  quantity  of  water  can  be  forced  in;  and  if 
the  tube  connected  with  the  pump  is  suddenly  opened  the 
India-rubber  division  will  fly  back  to  its  original  position, 
and  throw  out  the  water  just  as  the  inner  coating  was  dis- 
charged when  touched  with  the  finger. 

In  the  second  experiment  the  outer  coating  of  tin-foil 
was  in  connection  with  the  earth.  Now,  in  order  that  the 
electrical  machine  may  continue  to  give  a supply  of  elec- 
tricity, its  rubber  must  be  in  connection  with  the  earth; 
or  the  jar  may  be  insulated  and  its  outer  coating  connected 
with  the  rubber  of  the  machine,  the  inner  coating  remaining 


WHAT  WE  KNOW  ABOUT  ELECTRICITY 


15 


in  electrical  connection  with  the  prime  conductor.  To  rep- 
resent the  state  of  things  in  the  second  experiment  the  India- 
rubber  covrering  must  therefore  be  removed  from  the  further 
extremity  of  the  tube,  and  the  tube  allowed  to  dip  into  a 
tank  with  which  the  pump  is  also  in  connection;  or  the  tube 
representing  the  outer  coating  of  the  jar  may  be  connected 
directly  with  the  pump.  In  either  case,  when  the  pump  is 
worked,  water  will  be  forced  into  the  tube  representing  the 
inner  coating,  the  same  amount  being  simultaneously  with- 
drawn from  the  other  tube;  and  if  sufficient  force  is  applied, 
this  may  be  continued  until  the  India-rubber  division 
breaks.  Similarly,  in  case  of  the  jar,  given  a sufficiently 
powerful  machine,  the  electrification  may  be  increased  until 
the  electricity  either  overflows  or  discharges  through  the 
glass,  which  would  be  broken  in  the  process.  If  the  jar  is 
properly  constructed,  the  tin-foil  will  be  taken  up  so  near 
to  the  edge  that  the  discharge  when  it  takes  place  will  occur 
through  the  air,  round  the  edge  of  the  jar  instead  of  through 
the  glass,  thereby  saving  the  jar  from  destruction. 

This  experiment  illustrates  something  more  than  the  pre- 
vious ones — viz.,  it  not  only  shows  that  the  flow  of  electricity 
is  like  the  flow  of  a liquid,  but  that  it  is  like  the  flow  of  an 
incompressible  liquid;  so  that  in  order  to  force  electricity 
into  any  conductor  an  equal  amount  must  be  simultaneously 
forced  out  of  it.  If  this  explanation  of  the  action  of  a Ley- 
den jar  is  correct,  we  should  expect  the  glass,  or  other 
dielectric,  separating  two  charged  conductors,  to  be  in  a 
state  of  constraint,  and  this  has  been  conclusively  proved 
to  be  the  case  by  examining  the  glass  by  the  aid  of  polar- 
ized light. 

We  are  therefore  justified  in  concluding  that  whatever 
electricity  really  is,  it  behaves  exactly  as  if  it  were  an  incom- 


16 


ELECTRICITY  IN  MODERN  LIFE 


pressible  liquid;  and  it  follows  that  the  first  analogy  for  the 
production  of  electricity  by  friction  between  two  conductors 
would  have  been  more  exact  if  we  had  supposed  the  space 
above  the  pistons  in  the  jars  to  be  likewise  filled  with  water, 
and  the  whole  apparatus  to  be  immersed  in  a tank  of  water, 
when,  of  course,  instead  of  air  flowing  out  of  one  tube  into 
the  other,  we  should  have  water,  and  the  phenomena  might 
be  made  evident  by  the  aid  of  some  light  bodies  suspended 
in  the  water  near  the  open  ends  of  the  tubes.  Water  may 
be  forced  through  the  tube  in  various  ways;  but,  other  cir- 
cumstances being  the  same,  the  strength  of  the  current  of 
water — that  is  to  say,  the  quantity  which  passes  across  a sec- 
tion of  the  tube  in  unit  time — will  depend  upon  the  pressure, 
as  will  also  the  height  to  which  the  water  can  be  forced. 
Again,  if  the  vessels  containing  water  are  in  connection  by 
means  of  a tube,  no  flow  will  take  place  through  the  tube 
if  the  water  is  at  the  same  level  in  both  vessels;  but  if  it  is 
at  a higher  level  in  the  first  than  in  the  second,  the  water 
will  flow  along  the  tube  from  the  first  vessel  into  the  second 
until  the  levels  become  equal,  because,  as  long  as  the  level 
of  water  in  the  two  vessels  remains  unequal,  the  pressure 
from  the  first  vessel  to  the  second  will  be  greater  than  in  the 
opposite  direction.  Since  the  flow  of  electricity  may  be 
compared  to  the  flow  of  water,  we  should  expect  to  find 
something  analogous  to  difference  of  pressure  as  the  cause 
of  the  flow  of  electricity  from  one  conductor  to  another. 
This  has  already  been  found  to  be  the  case  in  charging  a 
Leyden  jar  by  means  of  an  electrical  machine,  what  may  be 
called  electrical  pressure  gradually  increasing  up  to  a certain 
limit  with  the  number  of  turns  given  to  the  machine;  and 
with  a large  machine  and  a small  jar  the  jar  might  be 
broken,  or,  if  properly  constructed,  made  to  overflow. 


WHAT  WE  KNOW  ABOUT  ELECTRICITY 


17 


With  a small  machine  and  a large  jar,  however,  it  would 
be  found  that  after  a certain  number  of  turns  no  further 
effect  whatever  would  be  produced,  showing  that  the  limit 
of  pressure  attainable  by  means  of  the  machine  has  been 
reached.  This  introduces  the  idea  of  what  is  called  elec- 
trical potential.  The  difference  of  potential  between  two 
conductors,  or  between  parts  of  the  same  conductor,  is  analo- 
gous to  difference  of  pressure,  due  to  difference  of  level  in 
the  case  of  water;  and  indeed  electrical  engineers  very  com- 
monly use  the  term  electrical  pressure  in  place  of  potential 
difference. 

Now,  water  can  only  flow  from  one  part  of  a vessel 
to  another  when  the  pressures  in  different  directions  are 
unequal;  but  this  difference  of  pressure  may  be  produced 
in  other  ways  than  by  difference  of  level.  In  the  same  way 
the  flow  of  electricity  may  be  produced  by  other  means  than 
difference  of  potential,  and  therefore  the  more  general  term, 
electro-motive  force,  usually  denoted  by  the  letters  B.M.F., 
is  employed,  being  defined  as  whatever  causes  motion  of 
electricity.  Potential  difference  is  therefore  a special  way 
of  producing  E.M.F.,  just  as  difference  of  level  is  a special 
way  of  producing  difference  of  pressure  in  the  case  of  water. 

It  must  not  be  forgotten  that  it  was  originally  decided  to 
call  vitreous  electricity  positive,  and  by  flow  of  electricity 
to  denote  a flow  of  positive  electricity — that  is  to  say,  using 
the  water  analogy,  we  suppose  positive  electrification  to  con- 
sist in  an  excess  of  water.  The  assumption  that  negative 
electrification  consists  in  an  excess  of  water  might  equally 
well  be  made,  for  although  it  has  been  shown  that  some- 
thing analogous  to  a flow  of  water  takes  place  in  a conductor 
which  is  undergoing  changes  in  electrification,  no  criterion 
has  been  obtained  to  determine  the  direction  of  the  flow. 


18 


ELECTRICITY  IN  MODERN  LIFE 


whicli  is  absolutely  unknown,  and  we  are  totally  ignorant 
also  of  the  velocity  of  flow,  which  may,  for  all  we  know,  be 
a million  miles  in  a second,  or  half  an  inch  in  a century. 

Friction  between  different  substances  is  not  at  all  a con- 
venient method  for  obtaining  an  electric  current  through  a 
conductor,  for  even  when  a very  large  frictional  machine 
is  used  only  very  weak  currents  can  be  obtained.  The  most 
convenient  method  of  producing  a current  for  ordinary  ex- 
perimental purposes  is  by  means  of  some  form  of  galvanic 
or  voltaic  cell — a convenient  form  of  cell  for  obtaining  fairly 
strong  currents  for  a short  time  is  the  well-known  Bichromate 
cell.  It  consists  of  a glass  vessel  containing  a solution  of 
bichromate  of  potash,  with  a slight  trace  of  sulphuric  acid, 
and  a plate  of  zinc  and  one  of  carbon,  or  more  frequently 
two  plates  of  carbon,  one  on  each  side  of  the  zinc,  immersed 
in  the  solution.  If  the  carbon  plates  or  plate  are  then  con- 
nected with  one  end  of  a wire  or  other  conductor,  while  the 
other  end  of  the  conductor  is  connected  with  the  zinc  plate, 
a current  of  positive  electricity  will  flow  from  the  carbon 
through  the  wire  to  the  zinc,  and  through  the  liquid  from 
the  zinc  to  the  carbon.  A single  cell  of  this  kind  holding 
about  a quart  of  solution  is  capable  of  maintaining  the  light 
of  a small  incandescent  lamp  for  some  three  or  four  hours. 
If  several  of  these  cells  are  joined  together  by  connecting 
the  carbon  of  one  to  the  zinc  of  the  next,  and  so  on,  the 
arrangement  is  called  a galvanic  or  voltaic  battery.  If  the 
reader  has  a battery,  say  of  four  or  five  such  cells,  and  a 
frictional  machine  at  command,  he  will  find  it  interesting  to 
compare  the  current  obtained  from  the  battery  with  that 
produced  by  the  frictional  electrical  machine.  If  the  rubber 
and  the  prime  conductor  of  the  machine  are  connected 
together  by  means  of  a piece  of  fine  platinum  or  iron  wire 


WHAT  WE  KNOW  ABOUT  ELECTRICITY 


19 


a few  inches  in  length,  no  effect  whatever  will  be  observed; 
but  if  the  same  wire  is  used  to  connect  the  last  two  zinc  and 
carbon  plates  of  the  battery,  it  will  be  raised  to  a white 
heat.  Now,  a current  of  electricity,  when  passing  through 
a wire  or  other  conductor,  always  develops  heat,  and  the 
reason  that  no  heat  is  observed  in  the  wire  connecting 
the  conductor  and  the  electrical  machine  is  simply  be- 
cause the  quantity  of  electricity  passing  is  too  small  to 
produce  any  perceptible  effect. 

If  now  two  copper  wires  are  connected  to  the  free  zinc 
and  carbon  of  the  battery,  and  their  ends  brought  together, 
a small  spark  will  be  seen  when  they  come  in  contact.  The 
length  of  this  spark  will  be  so  short  that  it  would  be  impos- 
sible to  measure  it,  while  with  an  electrical  machine  of 
moderate  size  there  would  be  no  difficulty  in  obtaining  a 
spark  several  inches  in  length. 

If,  again,  the  inner  and  outer  coatings  of  a Leyden  jar 
are  connected  with  the  rubber  and  prime  conductor  of  the 
machine,  and  the  handle  is  turned  for  some  time,  the  jar  will 
either  burst  or  overflow  if  the  machine  is  powerful  enough, 
and  if  not,  a strong  spark  will  be  obtained  from  the  jar  on 
connecting  its  inner  and  outer  coatings.  If  the  ends  of  the 
wires  from  the  battery  are  now  connected  with  the  inner  and 
outer  coatings  of  such  a jar,  it  will  be  found  that  however 
long  the  battery  may  be  left  on,  the  jar  will  not  overflow, 
nor  will  it  be  possible  to  get  a perceptible  spark  on  connect- 
ing its  two  coatings.  What  is  required  in  order  to  charge 
a Leyden  jar  is  not  so  much  a large  quantity  of  electricity 
as  a high  pressure,  to  use  the  language  of  an  engineer,  or  a 
high  potential  difference,  if  we  wish  to  speak  scientifically. 
The  electrical  machine  gives  a high  potential  difference  but 
a very  small  current,  while  the  battery  gives  a very  much 


20 


ELEOTBIOITY  IN  MODERN  LIFE 


larger  current  with  a much  smaller  difference  of  potential, 
or  lower  pressure;  indeed,  it  would  be  necessary  to  employ 
a battery  of  many  thousand  cells  in  order  to  get  a potential 
difference  equal  to  that  produced  by  even  a small  frictional 
machine. 


CHAPTER  II 

WHAT  WE  KNOW  ABOUT  MAGNETISM 

IT  has  been  known  since  very  early  times  that  a certain 
mineral,  commonly  called  lodestone,  possesses  two  very 
remarkable  properties.  In  the  first  place,  it  has  the 
power  of  attracting  iron,  and  in  a lesser  degree  some  other 
substances — more  especially  the  two  metals,  nickel  and 
cobalt — with  a force  which  is  greater  beyond  all  compari- 
son than  the  attraction  of  gravitation,  which  is  always  ex- 
erted between  two  portions  of  matter.  In  the  second  place, 
when  a portion  of  it  is  suspended,  so  that  it  can  turn  freely 
in  any  direction;  for  example,  if  it  is  hung  up  by  a thread 
passing  through  its  centre  of  gravity,  it  always  assumes 
a certain  definite  direction  at  a given  place  on  the  earth’s 
surface.  These  properties  may  be  communicated  to  pieces 
of  iron  or  steel  by  simply  rubbing  them  in  a certain  definite 
manner  with  a piece  of  lodestone.  In  the  case  of  very  soft 
iron,  however,  the  properties  so  communicated  are  very  soon 
lost  again. 

Any  substance  which  has  these  properties  is  called  a 
magnet,  and  the  action  of  communicating  this  property  to 
iron  is  called  magnetizing  it.  The  lodestone  is  a chemical 
compound  of  the  metal  iron  with  the  gas  oxygen,  and  on 
account  of  its  possessing  the  two  properties  mentioned  it 


WHAT  WE  KNOW  ABOUT  MAGNETISM 


21 


is  also  known  as  magnetic  iron  ore,  or  magnetic  oxide 

of  iron. 

Humboldt,  in  the  “Cosmos,”  tells  us  that  three  centuries 
before  the  Christian  era  the  Chinese  caravans  were  guided 
on  their  journeys  across  the  trackless  wastes  of  Tartary  by 
means  of  a little  human  figure  revolving  upon  a pivot,  and 
holding  in  its  outstretched  hand  a fragment  of  lodestone, 
so  placed  that  its  arm  always  pointed  to  the  south. 

Large  magnets  are  not  now  manufactured  by  rubbing 
iron  with  lodestone,  because,  as  explained  in  a later  chap- 
ter, the  electric  current  provides  a means  of  magnetizing 
iron  and  steel  very  much  more  powerfully  than  would  be 
possible  merely  by  aid  of  the  lodestone.  The  process  of 
magnetizing  by  rubbing  is  however  still  frequently  employed 
as  a convenient  method  of  making  small  magnets,  as  a piece 
of  steel  or  iron  may  be  magnetized  by  rubbing  it  with  any 
other  magnet,  whether  this  be  a lodestone  or  an  artificial 
magnet.  By  the  aid  of  a moderately  strong  magnet  and  a 
few  steel  sewing  needles,  it  is  easy  to  make  a series  of 
experiments  on  the  principal  properties  of  magnets. 

There  are  several  ways  in  which  a needle  may  be  rubbed 
with  a magnet  in  order  to  magnetize  it,  the  simplest  of  these 
being  to  stroke  the  needle  always  in  the  same  direction  from 
end  to  end  with  the  same  end  of  a steel  magnet  made  in  the 
shape  of  a straight  or  bent  bar.  If  two  needles  are  magne- 
tized in  this  way  and  hung  up  by  threads,  so  that  they  can 
move  freely,  or  if  they  are  fixed  in  small  slips  of  cork,  and 
allowed  to  float  on  the  surface  of  water,  it  will  be  found  that 
the  needles  will  turn,  so  that  two  definite  ends  are  juxta- 
posed, after  which  they  will  approach  each  other  until  they 
come  into  contact.  If  both  the  needles  are  reversed,  so  that 
the  opposite  ends  of  each  are  brought  together,  they  will 


22 


ELECTRICITY  IN  MODERN  LIFE 


again  attract  each  other;  but  if  one  of  the  needles  is  reversed 
the  needles  will  be  found  to  repel  each  other. 

Eepeat  this  experiment,  magnetizing  the  two  needles  by 
stroking  them  from  the  eye  to  the  point  with  one  end  of  the 
magnet  which  has  been  marked.  Then  hang  the  needles 
up,  and  it  will  be  found  that  the  two  points,  if  brought  to- 
gether, will  repel  each  other,  and  the  two  eyes,  if  brought 
together,  will  also  repel  each  other;  but  a point  and  an  eye 
will  attract  each  other.  It  is  clear,  therefore,  that  there  is 
a distinction  between  the  two  ends  of  the  needles,  and  also 
that  similar  ends  repel  each  other  while  dissimilar  ends  at- 
tract each  other.  The  ends  of  the  magnetized  needles  are 
commonly  called  poles. 

Bring  the  marked  end  of  the  magnet  which  was  used 
to  magnetize  the  needles  near  to  the  point  of  either  needle, 
suspended  by  its  thread,  and  it  will  be  found  that  the  nee- 
dle will  be  attracted,  showing  that  the  end  of  the  needle  last 
rubbed  by  the  magnet  becomes  of  opposite  polarity  to  that 
of  the  end  of  the  magnet  with  which  it  was  rubbed.  If  the 
marked  end  is  brought  to  the  eye  of  the  needle,  repulsion 
will  take  place.  The  unmarked  end  of  the  magnet  will  be 
found  to  attract  the  eye  of  either  needle  and  repel  the  point. 

Hang  up  a magnetized  needle  by  means  of  a thread  pass- 
ing through  its  centre  of  gravity,  which  should  have  been 
determined  before  it  was  magnetized,  since  the  process  of 
magnetization  tends,  as  has  been  pointed  out,  to  set  it  in  a 
certain  definite  position,  and  therefore  interferes  with  the 
determination.  The  needle  will  then  set  itself  in  a vertical 
plane,  making  a small  angle  with  the  plane  of  the  geographi- 
cal meridian,  and  the  end  of  the  magnet  which  turns  toward 
the  north  will  point  downward  toward  the  ground,  making 
an  angle  of  between  60"^  and  70°  with  the  horizon.  Suppose 


WHAT  WE  KNOW  ABOUT  MAGNETISM 


23 


that  the  marked  end  turns  toward  the  north,  this  is  then 
called  the  north,  or  north-seeking,  pole  of  the  magnet. 

If  the  original  magnet,  or  either  of  the  magnetized 
needles,  is  dipped  into  iron  filings,  it  will  attract  them, 
and  a number  of  iron  filings  will  adhere  to  each  end  of 
the  magnet;  but  it  will  generally  be  found  that  none  will 
adhere  to  the  middle. 

Bring  the  head  of  a soft  iron  nail  into  contact  with  the 
marked  pole  of  the  magnet,  and  it  will  be  found  that  as  long 
as  the  iron  nail  is  in  contact  with,  or  close  to,  the  end  of  the 
magnet  it  is  capable  of  attracting  iron  filings.  Moreover,  if 
one  of  the  suspended  needles  is  brought  near  to  the  point 
of  the  nail,  the  latter  will  be  found  to  attract  the  point  of 
the  needle,  and  repel  the  eye,  showing  that  the  nail  has  be- 
come a magnet,  and  that  the  end  in  contact  with  the  marked 
pole  of  the  magnet  has  become  a pole  dissimilar  to  the 
marked  pole.  If  a piece  of  hard  steel  were  used  instead 
of  the  iron  nail,  it  would  be  found  to  be  less  strongly  mag- 
netized while  in  contact  with  the  magnet;  but  on  removing 
it  from  the  neighborhood  of  the  magnet  it  would  be  found 
to  retain  all  its  magnetism,  while  the  soft  iron  nail  would 
have  lost  almost  every  trace.  The  process  of  magnetizing 
a piece  of  iron  by  bringing  it  into  the  neighborhood  of  a 
magnet  is  called  magnetic  induction. 

If  a long  steel  knitting-needle  is  magnetized  and  broken 
into  a number  of  pieces,  it  will  be  found  that  each  separate 
piece  is  a magnet,  and  that  the  ends  of  two  pieces  which 
were  originally  in  contact  are  of  opposite  polarity. 

This  suggests,  as  a possible  explanation  of  magnetic  in- 
duction, the  theory  put  forward  by  the  German  physicist, 
Weber.  This  theory  has  obtained  general  acceptance,  and 
may  now  be  considered  as  raised  from  the  rank  of  a hypoth- 

SCIENCE — VOL.  XIII — 2 


24 


ELECTRICITY  IN  MODERN  LIFE 


esis  to  that  of  an  established  fact.  I must  first  premise  that 
a substance  which  is  capable  of  experiencing  any  force  in 
virtue  of  the  magnetism  of  neighboring  bodies  is  called  a 
magnetic  substance.  Iron  is  beyond  all  comparison  the 
most  powerful  magnetic  substance.  After  iron,  and  a very 
long  way  after  it,  come  the  minerals  nickel  and  cobalt;  and 
the  sensitive  magnetic  instruments  which  are  now  in  the 
hands  of  investigators  indicate  that  it  is  almost  impossible 
to  find  any  substance  which  is  not  more  or  less  magnetic 
— that  is  to  say,  which  is  not  more  or  less  susceptible  to 
magnetic  action. 

Weber  supposes  that  every  one  of  the  molecules  of  which 
a magnetic  substance  is  built  up  is  itself  a magnet;  but  that 
the  axes  of  these  small  magnets  are  turned  in  every  possible 
direction.  The  ma;gnetic  actions  of  the  molecules  will  then 
neutralize  one  another,  so  that  the  body  will  not  act  as  a 
magnet;  but  if  either  pole  of  a magnet  be  brought  near  to 
it,  this  pole  will  attract  the  unlike  poles  of  the  molecules, 
and  will  repel  the  like  poles,  so  that  the  molecules  will  tend 
to  arrange  themselves  with  their  north  poles  pointing  one 
way  and  their  south  poles  pointing  the  other  way.  The 
molecules  will  then  act  together,  and  will  form  a magnet 
with  the  portion  nearest  to  the  pole  of  the  inducing  magnet 
of  unlike  polarity  to  it.  It  will  be  of  interest  to  consider 
one  or  two  experiments  which  help  to  establish  the  truth 
of  this  theory. 

Take  an  iron  or  steel  bar — such,  for  example,  as  a poker 
— and  hold  it  parallel  to  the  direction  assumed  by  a freely 
suspended  magnetic  needle;  we  should  expect,  if  the  poker 
were  built  up  of  magnetic  molecules,  that  each  molecule  would 
try  to  set  itself  in  a direction  parallel  to  that  of  the  sus- 
pended needle,  for  we  should  expect  the  earth  to  act  upon 


WHAT  WE  KNOW  ABOUT  MAGNETISM 


25 


each  molecule  in  exactly  the  same  way  in  which  it  acts 
upon  a suspended  magnet.  The  direction  assumed  by  a 
freely  suspended  magnet  in  this  part  of  the  world  is  not 
very  far  removed  from  the  vertical,  so  we  should  expect 
to  obtain  a fairly  good  result  by  simply  holding  the  poker 
in  a vertical  position.  Now,  if  the  poker  is  merely  held  for 
a few  moments,  either  parallel  to  the  suspended  magnetic 
needle,  or  simply  vertical,  and  then  tested  for  magnetism  by 
trying  whether  either  end  of  it  has  the  power  of  repelling 
either  end  of  a suspended  magnet,  it  will  be  found,  provided 
’ the  poker  was  not  magnetized  previous  to  the  experiment, 
that  it  will  not  have  acquired  any  sensible  magnetic  proper- 
ties. Steel  railings,  however,  which  have  remained  for  many 
years  in  a vertical  position  have  frequently  been  observed  to 
have  acquired  magnetic  properties,  the  lower  end  having  be- 
come a north  pole,  as  we  should  expect,  if  Weber’s  theory  is 
true.  Now,  it  must  be  remembered  that  all  the  molecules  of 
the  poker  are  closely  packed  together,  and  it  is  therefore 
quite  possible  that  the  earth  may  exert  a force  tending  to 
set  them  in  a definite  direction,  but  that  this  force  may  not 
be  strong  enough  to  overcome  the  cohesion  of  the  molecules. 
This  suggests  that  we  should  try  by  some  means  to  diminish 
the  cohesion  of  the  molecules,  and  see  if  any  better  results 
are  obtained.  One  way  of  doing  this  would  be  to  strike  the 
poker  with  a hammer,  and  it  will  be  found  that  if  the  poker 
is  held  vertical  and  struck  with  a hammer,  it  will  become 
a magnet,  the  lower  extremity  becoming  a north  pole ; and 
if  the  position  of  the  poker  is  reversed,  and  it  is  again  struck, 
its  magnetism  will  be  immediately  reversed.  Another  way 
of  diminishing  the  cohesion  would  be  to  make  the  poker 
red  hot;  and  it  will  be  found  that  if  the  poker  is  heated  to 
redness,  and  then  left  in  a vertical  position  until  it  becomes 


26 


ELECTRICITY  IN  MODERN  LIFE 


cool,  it  will  have  become  a magnet,  having  its  lower  ex“ 
tremity  a north  pole. 

It  has  been  observed,  moreover,  that  if  a body  is  magne- 
tized it  usually  becomes  either  slightly  longer  and  thinner, 
or  broader  and  thicker;  the  nature  of  the  change  depending 
partly  on  the  shape  of  the  body  and  partly  upon  the  state  of 
strain  in  which  it  happens  to  be  at  the  time  of  the  experi- 
ment. Another  fact  strongly  in  support  of  Weber’s  theory 
is  that  when  a piece  of  iron  is  suddenly  magnetized  or  de- 
magnetized by  means  of  an  electric  current,  a slight  sound 
is  heard,  which,  according  to  this  theory,  is  due  to  the  sud- 
den turning  of  the  molecules.  This  production  of  sound 
during  magnetization  and  demagnetization  was  utilized  in 
the  construction  of  one  of  the  earlier  forms  of  telephone 
receivers,  which  will  be  described  in  a later  chapter. 


MAGNETS  AND  CONDUCTORS 


27 


CHAPTER  111 

MUTUAL  ACTIONS  BETWEEN  MAGNETS  AND  CONDUCTORS 
TRAVERSED  BY  ELECTRIC  CURRENTS 

At  the  beginning  of  the  present  century  the  Swedish 
philosopher  Oersted  observed  that  when  a wire  carry- 
ing an  electric  current  was  held  over  and  parallel 
to  a compass  needle,  the  needle  was  deflected  to  the  right 
or  left,  the  direction  of  deflection  depending  on  that  of  the 
current.  When  the  wire  was  placed  underneath  the  needle, 
and  parallel  to  it,  while  the  direction  of  the  current  remained 
the  same,  the  direction  of  deflection  was  also  reversed. 
The  subject  was  shortly  afterward  taken  up  by  the  great 
mathematician  and  physicist.  Ampere,  who  found  that  the 
direction  of  deflection  was  such  that  to  a person  lying  along 
the  wire  with  the  current  going  from  his  feet  to  his  head,  the 
north  pole  of  the  needle  would  always  turn  to  his  left  hand. 
Ampdre  also  discovered  that  two  conductors  carrying  electric 
currents  attract  or  repel  each  other,  and  otherwise  behave 
just  like  magnets.  These  discoveries  are  of  the  greatest  im- 
portance, as  they  give  us  the  means  of  detecting  the  exist- 
ence of  electrical  currents,  and  of  measuring  their  strength 
by  means  of  magnetic  instruments.  I will  therefore  consider 
them  further. 

Suppose  that  a wire  has  been  bent  into  the  form  of  a 
circular  ring,  leaving  its  two  ends  free.  Let  the  two  ends 
be  connected  with  the  poles  of  a battery,  and  the  ring  sus- 


28 


ELECTRICITY  IN  MODERN  LIFE 


pended  from  a support  in  such  a manner  that  the  whole 
circle  can  turn  freely  in  any  direction.  It  will  then  be 
found  that  the  circle  will  place  itself  with  its  plane  per- 
pendicular to  the  direction  of  the  magnetic  dipping  needle, 
as  a freely  suspended  magnet  is  usually  called.  If  the  di- 
rection of  the  current  through  the  circuit  is  reversed,  the 
circle  will  again  take  up  a position  with  its  plane  perpen- 
dicular to  the  direction  of  the  magnetic  dipping  needle,  but 
its  aspect  will  be  reversed — the  face  that  before  pointed  to- 
ward the  north  now  pointing  toward  the  south.  If  the  direc- 
tion of  the  current  round  the  circle  in  each  case  is  noted,  it 
will  be  found  that,  looking  at  the  circle  from  the  south  side, 
the  current  will  flow  round  it  in  the  direction  of  the  hands  of 
a watch;  or,  as  we  say,  the  direction  of  flow  round  the  circle 
is  clockwise.  The  face  of  the  circuit  which  points  north- 
ward may  be  called  its  north  pole,  and  the  face  which  points 
southward  may  be  called  its  south  pole.  If  two  such  sus- 
pended circuits  are  brought  close  together,  they  will  be 
found  to  attract  when  opposite  poles  are  presented  to  each 
other,  and  to  repel  when  similar  poles  are  presented.  Thus, 
when  the  two  circles  are  parallel  to  each  other  they  will  at- 
tract, when  the  direction  in  which  the  current  flows  is  the 
same  in  both,  and  they  will  repel,  when  the  currents  flow  in 
opposite  directions  round  them.  It  is  found  generally  that 
conductors  carrying  parallel  currents  in  the  same  direction 
attract  each  other,  and  that  conductors  carrying  currents 
flowing  in  opposite  directions  repel  each  other.  Instead  of 
merely  a single  circle  a coil  of  any  form  may  be  used.  A 
coil  of  considerable  length  and  of  comparatively,  small  sec- 
tion is  a very  suitable  form.  Such  a coil  is  called  a solenoid. 

A number  of  experiments  of  this  nature  suggested  to 
Ampere  that  the  properties  of  magnets  might  be  accounted 


MAGNETS  AND  CONDUCTORS 


29 


for  by  assuming  that  every  molecule  of  a magnetic  substance 
had  an  electric  current  circulating  round  it.  When  a body 
was  magnetized  he  supposed  that  all  these  currents  were 
brought  into  parallelism.  In  this  case  the  currents  flowing 
in  opposite  directions  round  the  adjacent  portions  of  two 
molecules  would  destroy  each  other,  and  a magnetized  rod 
might  therefore  be  considered  as  equivalent  to  a series  of 
currents  flowing  in  the  same  direction  round  its  circum- 
ference; in  other  words,  it  would  be  exactly  like  a solenoid. 
Ampere’s  theory  of  magnetism  is  now  generally  accepted  as 
being  most  probably  true.  It  is  an  explanation  of  magnetic 
in  terms  of  electrical  action,  and  though  it  only  explains 
one  unknown  thing  in  terms  of  another,  it  has  the  advantage 
of  leaving  us  to  deal  with  one  unknown  quantity  instead  of 
with  two.  The  principal  difficulty  in  Ampere’s  theory 
of  magnetism  lies  in  the  fact  that  every  conductor  such  as 
we  are  acquainted  with  is  heated  when  traversed  by  an  elec- 
tric current,  whereas  Ampere’s  molecular  currents  must  flow 
round  the  molecules  without  causing  any  development  of 
heat,  otherwise  a magnetic  substance  would  afford  a con- 
tinuous supply  of  heat,  which  of  course  would  be  in  total 
opposition  to  experience.  So  little,  however,  is  known  about 
the  manner  in  which  this  heating  effect  is  produced,  owing 
to  our  total  ignorance  of  the  internal  structure  of  molecules, 
that  there  is  really  no  reasonable  ground  for  assuming  that 
the  effects  produced  in  the  two  cases  would  be  similar  in 
their  character. 

The  discovery  of  the  effect  of  an  electric  current  upon  a 
suspended  magnetic  needle  gave  a simple  means  of  detecting 
electric  currents  of  moderate  strengtli,  and  it  was  very  soon 
found  that  by  making  a current  flow  many  times  round  the 
needle,  instead  of  simply  passing  over  or  under  it,  the  effect 


^0 


ELECTRICITY  IN  MODERN  LIFE 


could  be  greatly  increased.  In  this  way  it  became  possible 
to  construct  instruments  capable  of  measuring  extremely 
feeble  currents.  Such  an  instrument  is  known  as  a galvanom- 
eter. If  a steel  bar  is  placed  within  a coil  of  wire  traversed 
by  an  electric  current — that  is  to  say,  a solenoid — the  bar  on 
being  removed  from  the  solenoid  will  be  found  to  be  mag- 
netized. If  a current  goes  round  the  solenoid  in  the  direc- 
tion of  the  hands  of  a watch  with  its  face  directed  toward 
the  end  from  which  the  current  flows,  the  end  of  the  steel 
bar  within  the  end  of  the  solenoid  at  which  the  current 
leaves  will  be  found  to  be  a north  pole  and  the  other  end  a 
south  pole.  This  is  easily  explained  on  Weber’s  theory; 
for  if  each  molecule  of  which  the  magnetic  substance  is 
built  up  is  turned  with  its  magnetic  axis  in  the  direction 
indicated  by  Ampere’s  rule,  previously  quoted,  it  will 
follow  that  when  a current  flows  over,  and  at  right  angles 
to,  a bar  of  steel  the  bai^  will  be  magnetized  in  such  a 
manner  that  a person  lying  along  the  wire,  with  the  current 
coming  in  at  his  heels  and  going  out  at  his  head,  and  look- 
ing toward  the  bar,  will  see  the  north  pole  on  his  left  hand. 
The  reader  will  easily  see  that  this  agrees  with  the  result 
obtained  with  the  solenoid. 

Not  very  many  years  after  Ampere’s  discoveries  our  own 
great  physicist,  Michael  Faraday,  discovered  that  momentary 
electric  currents  were  produced  in  a conductor  which  was 
changing  its  position  relatively  to  a magnet,  or  to  a con- 
ductor carrying  an  electric  current.  Some  of  his  experi- 
ments we  must  consider  in  detail,  as  they  have  provided  a 
method  of  producing  electric  currents  of  almost  any  desired 
strength  very  much  more  cheaply  than  would  be  possible 
with  any  form  of  voltaic  battery.  Take  some  copper  wire 
covered  with  gutta  percha  or  cotton,  or  other  insulating 


MAGNETS  AND  CONDUCTORS 


31 


substance,  wind  it  into  a coil,  and  connect  the  ends  with 
the  terminals  of  a galvanometer — that  is  to  say,  with  the 
extremities  of  the  wire  which  is  wound  round  the  suspended 
magnet.  Now  take  a strong  bar  magnet  and  push  it  right 
through  the  coil.  The  galvanometer  needle  will  then  sud- 
denlv  deflect,  first  in  one  direction  and  then  in  another, 
showing  that  during  the  passage  of  the  first  half  of  the  mag- 
net through  the  coil  a current  is  produced  in  one  direction, 
while  the  passage  of  the  other  half  gives  rise  to  a current  in 
the  opposite  direction.  This  shows  that  the  approach,  say 
of  the  north  pole  of  the  magnet  to  one  face  of  the  coil,  pro- 
duces a current  in  the  same  direction  as  its  recession  from 
the  opposite  face,  and  that  the  currents  produced  by  the 
approach  or  recession  of  the  north  and  south  poles  respec- 
tively are  in  opposite  directions.  Exactly  similar  effects  are 
produced  if  a coil  carrying  an  electric  current  is  used  in 
place  of  the  magnet;  but  this  is  not  all.  Faraday  found 
that  not  only  were  momentary  currents  produced  in  a con- 
ductor by  the  approach  or  withdrawal  of  a conductor  trav- 
ersed by  a current,  but  that  when  the  current  arises  or  dies 
away  in  a conductor  it  produces  a current  of  short  duration 
in  neighboring  conductors.  If  two  wires  are  placed  parallel 
to  each  other,  and  if  the  ends  of  one  wire  are  joined  so  as  to 
make  a complete  metallic  circuit,  while  an  electric  current 
is  suddenly  started  in  the  other,  by  connecting  its  ends  with 
the  poles  of  a battery,  a momentary  current  in  the  opposite 
direction  will  be  produced  in  the  first  conductor;  and  when 
the  battery  circuit  is  broken  there  will  be  a second  momen- 
tary current  produced  in  the  neighboring  conductor  in  a 
direction  opposite  to  the  previous  one.  These  momentary 
currents  are  called  induction  currents,  and  the  circuit  which 
produces  this  phenomenon,  either  by  its  motion  or  by  a cur- 


32 


ELECTRICITY  IN  MODERN  LIFE 


rent  being  excited  or  dying  away  within  it,  is  called  the 
primary  circuit,  while  that  in  which  the  momentary  current 
is  produced  is  called  the  secondary  circuit. 


CHAPTER  IV 

FOECE,  WORK,  AND  POWER 

IN  order  to  understand  the  conditions  which  determine 
the  relative  advantages  of  different  methods  of  pro- 
ducing and  distributing  the  electric  current,  a clear  idea 
of  the  physical  quantities.  Force,  Work,  and  Power,  must 
first  be  obtained.  Newton  defines  a force  as  whatever  causes 
change  in  the  motion  of  a portion  of  matter.  Thus,  when  a 
train  is  at  rest  at  a station,  a certain  force  has  to  be  applied 
to  set  it  in  motion  and  to  increase  its  speed;  force  is  also 
required  to  stop  the  train  when  once  it  is  in  motion,  as  is 
shown  in  a very  forcible  manner  if  it  comes  into  collision 
with  a stationary  or  moving  body,  such  as,  for  example, 
another  train.  When  once  the  train  has  got  up  its  required 
speed,  it  would  continue  to  move  at ‘that  speed,  if  there 
were  no  force  tending  to  bring  it  to  rest,  and  therefore,  if 
this  were  the  case,  a train  running  along  a level  line  would 
only  require  an  engine  to  start  it,  after  which  it  would  con- 
tinue to  move  without  further  application  of  force  until 
means  were  taken  to  bring  it  to  rest. 

As  everybody  knows,  however,  no  train  will  continue  to 
run  on  indefinitely  without  assistance  from  the  engine,  and 
therefore  there  must  be  some  one  or  more  forces  acting  upon 
it  in  such  a way  as  to  retard  its  motion.  The  chief  of  these 
is  the  friction  between  the  moving  parts.  It  is  unfortunately 


FORCE,  WORK,  AND  POWER 


83 


impossible  to  obtain  any  body  in  nature  which  is  not  already 
acted  upon  by  some  force,  so  that  when  a certain  force  is 
applied  to  a body,  it  is  impossible  to  determine  its  effect 
directly,  because  it  is  mixed  up  with  those  of  the  forces 
already  acting  upon  the  body;  and  it  is  only  by  a careful 
study  of  the  motion  of  bodies  under  various  conditions  that 
it  becomes  possible  to  distinguish  the  different  forces  acting 
upon  them,  and  to  determine  which  of  the  effects  are  due  to 
each  force. 

It  was  by  continued  observations  of  this  kind  that  Sir 
Isaac  Newton  came  to  the  conclusion  that  if  a body  could 
be  found  which  was  acted  on  by  no  force,  it  would  either 
remain  at  rest  or  continue  to  move  at  a uniform. rate  in  a 
straight  line.  Newton  also  found  that  if  a single  force  acted 
upon  a body  at  rest,  it  would  cause  it  to  move  with  a con- 
tinually increasing  velocity  in  the  direction  of  the  force. 
He  found  that  as  long  as  the  force  remained  the  same  the 
increase  in  the  velocity  of  the  body  during  each  second  for 
which  the  force  was  applied  was  the  same,  and  he  also  found 
that  the  force  required  to  increase  the  velocity  of  a body 
by  a given  amount  in  a given  time  was  proportional  to  the 
quantity  of  matter  contained  in  the  body,  or  what  is  known 
as  its  mass. 

The  general  idea  of  force  is  a familiar  one,  but  these 
exact  statements  about  it  are  necessary  in  order  to  be  able 
to  measure  force,  and  indeed  no  one  can  ever  be  said 
really  to  understand  the  meaning  of  any  quantity  unless 
he  is  able  to  measure  it — that  is  to  say,  to  make  an  exact 
numerical  comparison  between  different  quantities  of  the 
same  kind.  The  statements  which  I have  made  about 
the  nature  of  force  do  give  the  means  of  measuring  it.  For 
example,  suppose  that  we  have  a body,  the  mass  of  which 


84 


ELECTRICITY  IN  MODERN  LIFE 


is  one  pound,  and  suppose  that  this  body  can  be  removed 
from  the  action  of  all  forces,  such  as  the  attraction  of  the 
earth,  the  resistance  of  the  air,  and  so  on.  Apply  to  this 
body  during  the  interval  of  one  second  a force  which  will 
make  it  move  at  a rate  of  one  foot  in  a second.  Then  we 
are  able  to  state  from  what  has  gone  before  that  to  give  the 
same  velocity  to  a mass  of  two  pounds  we  should  have  to 
apply  double  the  force  for  a second,  or  the  same  force  for 
two  seconds. 

In  order  to  measure  any  quantity,  it  must  be  compared 
with  some  other  quantity  of  the  same  kind.  For  example, 
if  we  say  that  a certain  distance  is  ten  miles,  what  we  mean 
is  that  the  distance  is  ten  times  as  great  as  some  other  dis- 
tance with  which  we  are  acquainted  and  which  we  call  a 
mile.  The  mile  is  said  to  be  the  unit,  in  terms  of  which  the 
distance  is  measured;  and  if  the  distance  is  to  be  measured 
in  miles  it  will  be  completely  determined  by  a mere  number, 
such  as  ten  or  fifty.  It  is  clear  then  that  the  expression  of 
any  physical  quantity  must  contain  a unit,  consisting  of  a 
certain  quantity  of  the  same  kind  previously  decided  on,  and 
a number  expressing  how  many  times  the  unit  is  contained 
in  the  quantity.  Now,  apply  this  to  the  measurement  of 
force. 

The  unit  of  force  in  use  for  ordinary  engineering  pur- 
poses is  the  weight  of  a pound — that  is  to  say,  the  force  with 
which  the  earth  draws  a mass  of  one  pound.  The  principal 
objection  to  this  unit  is  that  the  pull  exerted  by  the  earth 
upon  any  mass  varies  slightly  from  place  to  place  on  the 
earth’s  surface,  being  greatest  at  the  North  and  South  Poles, 
and  least  at  the  Equator;  so  that  where  great  exactnesses 
required,  the  place  of  observation  must  be  stated.  This  unit 
has  therefore  not  been  adopted  for  electrical  measurements. 


FORCE,  WORK,  AND  POWER 


35 


nor  has  any  other  unit  founded  upon  the  English  measures 
of  mass  and  length.  For  scientific  purposes  the  French 
metrical  system  is  now  universally  adopted,  and,  the  system 
of  electrical  measurement  being  a comparatively  recent  de- 
velopment, the  importance  of  having  our  electrical  measure- 
ments given  in  terms  of  the  same  unit  as  employed  in  other 
countries  has  decided  British  electrical  engineers  to  adopt 
units  founded  on  the  metrical  system. 

According  to  this  system,  the  unit  of  force,  which  is 
called  the  dyne,  is  defined  as  the  force  which,  when  applied 
for  one  second  to  a mass  of  one  gramme,  will  give  it  a 
velocity  of  one  centimetre  per  second.  This  is  what  is  called 
an  absolute  unit — that  is  to  say,  it  does  not  vary  with  the 
place  or  time  of  observation,  but  depends  only  on  the  three 
fundamental  units — namely,  the  second,  which  is  in  use  all 
over  the  world,  and  the  centimetre  and  gramme,  which  are 
determined  by  comparison  with  the  standard  metre  and  the 
standard  kilogramme  which  are  kept  in  Paris. 

The  next  step  is  to  obtain  an  exact  idea  of  what  is  meant 
by  a quantity  of  work.  If  a body  moves  under  the  action 
of  a force,  work  is  said  to  be  done  by  the  body,  and  the 
amount  of  work  done  is  measured  by  the  product  of  the  force 
into  the  distance  through  which  the  body  moves  in  the  direc- 
tion of  the  force.  If  a body  is  moved  against  any  force,  work 
is  said  to  be  done  on  the  body,  and  its  amount  is  measured 
by  the  product  of  the  force  into  the  distance  moved  in  a 
direction  opposite  to  that  of  the  force.  For  ordinary  engi- 
neering purposes,  where  the  pound  weight  is  taken  as  the 
unit  of  force,  the  unit  of  work  is  defined  as  the  amount  of 
work  required  to  lift  a mass  of  a pound  to  a height  of  a foot, 
and  is  called  a foot-pound.  The  foot-pound  being  expressed 
as  the  product  of  a pound  weight  into  a length  of  a foot, 


36 


ELECTRICITY  IN  MODERN  LIFE 


must,  of  course,  like  the  pound  weight,  vary  from  place 
to  place  on  the  earth’s  surface.  The  absolute  unit  of  work 
employed  for  electrical  measurement,  and  for  all  scientific 
purposes,  is  the  work  done  by  a force  of  one  dyne  acting 
in  its  own  direction  through  a distance  of  one  centimetre. 
This  unit  of  work  is  called  an  Erg. 

When  work  is  done  upon  a body  it  is  found  that  the 
body  is  afterward  capable  of  doing  exactly  the  same  amount 
of  work  that  has  been  done  upon  it,  and  it  is  therefore  said 
to  have  energy  stored  up  in  it,  energy  being  defined  as 
capacity  for  doing  work.  Thus,  if  a cannon-ball  weighing 
a thousand  pounds  were  lifted  to  the  height  of  one  hundred 
feet,  a hundred  thousand  foot-pounds  of  work  would  have 
to  be  done  upon  it.  If  the  body  were  then  allowed  to  drive 
a machine  during  its  fall,  it  would  do  exactly  the  same 
amount  of  work  by  the  time  it  had  returned  to  its  original 
level. 

It  used  to  be  thought  that  in  a process  of  this  kind  some 
of  the  work  was  lost;  in  other  words,  that  the  ball  in  de- 
scending would  not  do  as  much  work  as  was  required  to 
lift  it,  for  it  could  not,  by  any  arrangement,  be  made  to  lift 
another  ball,  of  equal  weight,  to  the  same  height.  The 
reason  of  this  is,  that  some  of  the  work  is  always  wasted  in 
some  such  way  as  overcoming  friction,  or  the  resistance 
of  the  air.  In  either  case  a certain  amount  of  heat  is  gen- 
erated, and  it  has  been  shown  that  to  a certain  quantity 
of  heat,  generated  by  means  of  friction  or  other  mechanical 
means,  there  always  corresponds  a perfectly  definite  expendi- 
ture of  work,  so  that  heat  is  simply  another  form  of  energy. 
Just  as  mechanical  work  can  be  transformed  into  heat,  so 
heat  can  be  transformed  into  mechanical  work,  but  there 
is  this  important  dift'erence  between  the  two  cases:  there  is 


FORCE,  WORK,  AND  POWER 


37 


no  practical  difficulty  in  entirely  transforming  a certain 
amount  of  energy  in  the  form  of  mechanical  work  into  heat, 
but  it  is  impossible,  by  any  means  at  our  disposal,  to  trans- 
form the  whole  of  a given  quantity  of  heat  back  into 
mechanical  energy. 

These  considerations  give  us  a glimpse  of  two  principles 
of  the  greatest  importance  in  the  study  of  natural  phe- 
nomena. The  first  of  these  is  called  the  “Conservation  of 
Energy,”  and  it  asserts  that,  as  the  result  of  far-reaching 
experience,  it  is  found  that  whenever  energy  disappears  in 
one  form  it  reappears  without  loss  in  another.  This  impor- 
tant principle  was  first  stated  in  definite  terms  by  Professor 
von  Helmholtz  some  forty  years  ago,  and  has  been  fully 
confirmed  by  all  subsequent  experience,  so  that  it  now  ranks 
as  one  of  the  most  firmly  established  facts  of  nature.  This 
is  not  the  place  for  a detailed  discussion  of  the  conservation 
of  energy,  but  it  will  be  of  interest  to  point  out  in  passing 
that  the  principal  source  from  which  the  energy  necessary 
for  the  existence  of  our  world  is  derived  is  the  sun.  The 
heat  of  the  sun’s  rays  evaporates  the  water  of  the  ocean,  and 
the  moisture  thus  carried  up  into  the  atmosphere  becomes 
condensed  and  falls  again  in  the  form  of  rain,  and  so  feeds 
the  rivers,  which  may  be  utilized  to  drive  machinery  by 
means  of  water-wheels,  as  they  flow  back  to  the  sea.  The 
sun’s  rays,  again,  build  up  the  mineral  constituents  of  the 
earth’s  surface  into  the  various  forms  of  animals  and  plants, 
so  that  the  forests  and  the  coalfields  are  simply  great  store- 
houses of  the  energy  given  out  by  the  sun  in  past  ages, 
which  energy  is  utilized  when  the  wood  or  coal  is  burned; 
for  the  process  of  combustion  simply  consists  in  a recombi- 
nation between  the  oxygen  of  the  atmosphere  and  the  other 
elements  contained  in  the  wood  or  coal,  which  were  separated 


88 


ELECTRICITY  IN  MODERN  LIFE 


from  the  oxygen  with  which  they  were  before  combined, 
and  built  up  into  the  trees  of  the  forest,  simply  by  the 
energy  of  the  sun’s  rays. 

The  other  principle  to  which  I referred  is. known  as  the 

“Dissipation  of  Energy.”  It  is  found  that  in  every  process 

by  which  a transformation  of  energy  can  be  effected  there 

exists  a tendency  toward  an  ultimate  transformation  into 
€/ 

heat  of  low  temperature,  from  which  it  is  impossible,  by  any 
known  process,  to  obtain  other  useful  forms  of  energy.  This 
principle  certainly  applies  to  our  own  experience;  but  this 
experience  is  very  much  more  limited  than  that  from  which 
the  law  of  conservation  of  energy  is  deduced,  and  it  may  be 
that  there  are  natural  processes,  at  present  unknown,  which 
are  capable  of  transforming  this  low  temperature  heat  into 
some  of  the  other  known  forms  of  energy.  If  this  is  not 
the  case,  and  the  dissipation  of  energy  is  really  a universal 
law  of  the  universe,  then  the  time  must  come  when  the 
whole  universe  will  be  one  vast  inert  mass  of  uniform  tem- 
perature, and  therefore  without  life  or  any  form  of  motion. 

The  term  “Power”  is  used  by  engineers  to  denote  the 
rate  at  which  work  is  done.  The  power  of  a steam  engine 
is  usually  expressed  in  terms  of  the  horse-power  as  unit,  an 
engine  being  said  to  be  of  one  horse-power  when  it  is  capable 
of  doing  work  at  such  a rate  as  to  be  able  to  lift  33,000 
pounds  one  foot  high  in  one  minute.  It  may  be  as  well 
here  to  point  out  that  this  is  what  is  called  Indicated  Horse- 
power, and  is  usually  denoted  by  the  letters  I.H.P.  It  is 
determined  by  means  of  an  instrument  called  a “Steam 
Engine  Indicator,”  which  draws  a curve  representing  by  its 
area  the  product  of  the  length  of  stroke  of  the  piston  into 
the  average  pressure  of  the  steam  upon  it — that  is  to  say,  the 
work  done  at  each  stroke  of  the  engine — and  therefore  gives 


FORCE,  WORK,  AND  POWER 


39 


the  rate  of  doing  work  when  an  engine  is  making  a given 
number  of  revolutions  per  minute. 

When  a steam  engine  has  to  drive  a number  of  machines 
— such,  for  example,  as  dynamos  for  producing  the  electric 
current,  which  are  not  always  all  running  at  the  same  time — 
the  rate  of  working  of  the  engine  is  controlled  by  means  of  a 
governor,  which  shuts  off  a portion  of  the  steam  when  some 
of  the  machines  are  stopped,  or,  as  engineers  say,  when  a 
portion  of  the  load  of  the  engine  is  taken  off.  In  this  way 
the  engine  is  made  to  work  exactly  at  the  rate  required  at 
any  moment.  When  the  current  from  the  dynamos  is  used 
directly  for  producing  the  light  in  the  lamps,  it  is  of  very 
great  importance  to  maintain  the  power  of  the  engine  con- 
stant within  very  narrow  limits,  as  if  this  were  not  done  the 
speed  of  the  dynamos  would  vary,  and  this  would  produce 
a corresponding  variation  in  the  strength  of  the  light — that 
is  to  say,  it  would  give  rise  to  flickering.  In  order  to  ob- 
viate this,  very  sensitive  governors  should  be  used;  but 
even  with  the  most  sensitive  governors  available  it  would 
be  impossible  to  maintain  the  light  perfectly  steady  unless 
the  regulation  of  the  engine  were  supplemented  by  some  elec- 
trical device  for  directly  regulating  the  current  actually 
given  out  by  the  dynamo.  I shall  have  something  further 
to  say  about  these  methods  of  electrical  regulation  in  a later 
chapter,  as  the  subject  is  one  of  very  great  importance,  and 
the  great  improvement  in  the  steadiness  of  the  lamps  now 
in  use  over  those  of  a few  years  ago  is  to  a large  extent  due 
to  the  adoption  of  improved  methods  of  electrical  regulation. 

The  unit  of  power  employed  for  electrical  measurements 
is  called  the  “Watt,”  after  the  great  engineer  of  that  name. 
Its  value,  as  defined  electrically,  will  be  given  in  a later 
chapter,  and  it  will  be  sufficient  for  the  present  to  state  that 


40 


ELECTRICITY  IN  MODERN  LIFE 


a Watt  is  the  power  developed  when  44J  foot-pounds  of 
work  are  done  in  a minute,  so  that  746  Watts  are  equivalent 
to  a horse-power.  This  relation  is  not  absolutely  exact, 
because  the  Watt  is  an  absolute  unit  of  power,  while  the 
horse-power  depends  on  the  weight  of  the  pound,  and  there- 
fore varies  slightly  from  place  to  place  on  the  earth’s  sur- 
face; but  it  is  sufficiently  exact  for  all  purposes  for  which 
power  is  expressed  in  terms  of  horse-power. 

A term  in  frequent  use  in  connection  with  engines,  and 
which  the  reader  may  meet  with  in  accounts  of  electric  in- 
stallations as  descriptive  of  the  engine  power  employed, 
is  Nominal  Horse-power,  usually  denoted  by  the  letters 
N.H.P.  This  is  a very  indefinite  term,  as  it  is  a quantity 
depending  on  the  length  of  the  stroke  and  the  dimensions  of 
the  cylinder;  and  its  relation  to  the  indicated  horse-power 
which  can  be  given  out  by  the  engine  varies  very  much 
with  the  type  of  engine.  In  the  case  of  the  engines  used 
for  electric  light  purposes,  however,  the  maximum  l.H.P. 
should  be  in  general  about  three  times  the  N.H.P. , so  that 
an  engine  of  30  horse-power  nominal  should  be  capable, 
when  working  up  to  its  full  capacity,  of  giving  out  about 
90  horse-power.  The  reader  should  be  careful  to  distin- 
guish between  work  and  power,  and  remember  that  power 
is  the  rate  of  doing  work.  Confusion  between  these  terms  is 
often  made  even  by  persons  who  ought  to  know  better,  and 
it  is  clearly  not  an  unimportant  distinction ; for  to  define  the 
capacity  of  an  engine,  what  we  want  to  know  is,  how  much 
work  it  can  do  in  a given  time.  If  it  is  merely  stated  that 
an  engine  can  do  so  much  work,  without  stating  how  long  it 
takes  to  do  it,  we  are  given  no  information  whatever  as  to 
the  capacity  of  the  engine,  for  an  engine  employed  to  drive 
a small  lathe  which  might  be,  say,  of  half  horse-power,  may. 


SOURCES  OF  ELECTRICITY 


41 


if  kept  pretty  constantly  at  work,  do  a larger  amount  of  work 
in  the  course  of  twenty  years  than  the  engines  of  an  Atlantic 
liner,  of  perhaps  several  thousand  horse-power,  would  do  in 
twenty  minutes. 


CHAPTER  V 

SOURCES  OF  ELECTRICITY 

An  electric  current  is  a source  of  energy — that  is  to 
say,  it  is  capable  of  doing  work.  This  is  clear 
from  its  power  of  evolving  heat,  which,  as  1 have 
pointed  out,  is  a form  of  energy;  and  later  on  it  will  be 
shown  that  electrical  energy  may  be  transformed  directly 
into  mechanical  work.  According,  therefore,  to  the  princi- 
ple of  conservation  of  energy,  we  cannot  expect  to  maintain 
an  electric  current  without  keeping  up  a constant  supply 
of  energy.  The  simplest  way  of  considering  the  different 
sources  of  electricity  will  be  to  divide  them  first  into  two 
main  divisions,  according  to  the  kind  of  energy  which  is  em- 
ployed to  maintain  the  current.  These  two  kinds  of  energy 
are — (1)  Mechanical  Work  and  (2)  Energy  of  Chemical  Ac- 
tion. The  principal  kinds  of  apparatus  in  which  the  supply 
of  energy  is  in  the  form  of  mechanical  work  are — (1)  fric- 
tional machines,  (2)  influence  machines,  (3)  magneto  ma- 
chines, (4)  dynamos.  The  apparatus  coming  under  the 
second  heading  are  the  different  forms  of  galvanic  or  vol- 
taic batteries,  now  more  generally  known  as  primary 
batteries.  Heat  energy  may  also  be  used  to  maintain  an 
electric  current  by  means  of  an  apparatus  called  a thermo- 
electric battery.  This  source  of  energy  has  as  yet  been  very 
little  employed  for  generating  electric  currents  for  practical 


42 


ELECTRICITY  IN  MODERN  LIFE 


purposes,  but  it  is  not  improbable  that,  as  our  knowledge 
advances,  more  economical  means  of  generating  thermo- 
electric currents,  as  they  are  called,  may  be  discovered, 
and  energy  in  the  form  of  heat  may  then  be  much  more 
extensively  employed  for  maintaining  electric  currents  for 
commercial  purposes.  It  must  be  borne  in  mind  that  these 
distinctions  between  the  forms  in  which  energy  is  supplied 
to  different  classes  of  apparatus  is  one  merely  adopted  for 
convenience,  and  not  one  resting  upon  any  fundamental 
principle.  It  applies,  moreover,  only  to  the  source  from 
which  the  energy  is  derived  immediately  before  supplying 
it  to  the  apparatus.  For  example,  frictional  and  influence 
machines  are  generally  worked  by  hand.  Here  the  energy 
is  in  the  form  of  mechanical  work;  but  this  has  previously 
been  stored  up  in  the  human  body  in  the  form  of  chemical 
energy,  obtained  from  the  food  assimilated  by  the  body;  and 
this  chemical  energy  was  in  its  turn  obtained,  as  already  ex- 
plained, from  the  energy  stored  up  in  the  sun.  Dynamos, 
again,  are  usually  driven  by  steam-power,  or  sometimes, 
when  available,  by  water-power.  In  the  former  case  the 
source  of  energy  is  chemical  action — namely,  the  combus- 
tion of  the  coal;  in  the  second,  it  is  mechanical  work  due 
to  the  water  seeking  its  own  level  under  the  action  of  the 
force  of  gravity.  In  each  case,  as  explained  in  Chapter 
IV.,  the  energy  is  ultimately  derived  from  the  sun. 

Frictional  Machines 

The  frictional  machine  has  already  been  alluded  to  in 
Chapter  I.  It  used  to  be  employed  to  a considerable  extent 
for  producing  the  electricity  required  to  fire  charges  of  ex- 
plosives— as,  for  example,  in  blasting  operations.  At  pres- 
ent it  is  being  almost  entirely  displaced  by  the  influence 


SOURCES  OF  ELECTRICITY 


43 


machine,  and  I shall  therefore  not  devote  space  to  the  de- 
scription of  any  of  the  forms  of  instruments  employed  for 
such  practical  purposes.  The  most  convenient  form  of  the 
machine  for  experimental  purposes  is  what  is  called  the 
plate  electrical  machine.  It  consists  of  a disk  of  plate  glass 
mounted  upon  an  axle,  about  which  it  can  be  made  to  rotate 
by  means  of  a handle.  Eubbers,  usually  formed  of  leather 
or  silk,  are  attached  to  the  framework  on  which  the  axle  is 
supported  in  such  a way  that  they  press  against  opposite 
sides  of  the  upper  and  lower  edges  of  the  plate  respectively. 
At  a distance  of  90  degrees  from  each  of  these  rubbers  there 
is  fixed  a bent  brass  rod  surrounding,  but  not  touching,  the 
edge  of  the  plate,  and  furnished  on  the  side  presented  to- 
ward the  plate  with  small  projecting  spikes.  These  two 
bent  rods  are  attached  to  the  ends  of  a thick  brass  con- 
ductor, supported  upon  an  insulating  stand,  usually  made 
of  glass.  This  is  known  as  the  prime  conductor.  It  need 
not  have  any  special  form,  except  that  every  part  of  it  must 
be  rounded,  with  the  exception  of  that  presented  toward  the 
glass  plate.  The  reason  of  this  is  that  it  is  found  experi- 
mentally that  the  electrification  of  a conductor  always  dis- 
tributes itself  entirely  upon  the  surface  of  the  conductor, 
and  in  such  a manner  that  the  accumulation  of  electricity 
is  always  greatest  at  the  most  pointed  portions,  and  least  at 
the  most  rounded  portions.  Now  I have  pointed  out  that 
the  electricity  upon  any  conductor  tends  to  drive  away  the 
electricity  of  another  conductor  in  the  neighborhood,  and 
we  should  therefore  naturally  expect  the  electricity  of  a 
conductor  to  behave  in  exactly  the  same  way  toward  other 
electricity  in  the  same  conductor.  This  we  find  to  be  the 
case,  so  that  at  every  point  of  a conductor  there  is  a force 
acting  upon  the  electricity  of  the  conductor,  and  directed 


44 


ELECTRICITY  IN  MODERN  LIFE 


outward  from  it,  which  tends  to  break  down  the  insulation 
of  the  air  or  other  dielectric  surrounding  the  conductor,  and 
to  cause  the  escape  of  the  charge.  This  force  is  greatest 
where  the  accumulation  is  greatest — that  is  to  say,  at  the 
most  pointed  portions.  It  follows,  therefore,  that  all  the 
portions  of  the  conductor  should  be  rounded,  except  those 
facing  the  glass  disk,  for  here  we  wish  to  facilitate  the  flow 
of  electricity  between  the  conductor  and  the  glass. 

Before  using  the  machine,  a little  amalgam  of  mercury 
and  tin  rubbed  up  with  some  tallow  is  smeared  over  the 
rubbers,  as  it  is  found  that  this  greatly  favors  the  produc- 
tion of  electricity.  When  the  handle  is  turned,  and  the 
glass  plate  revolves,  it  becomes  electrified  positively  by 
friction  against  the  rubbers.  The  rubbers  at  the  same  time 
lose  positive  electricity,  and  to  supply  this,  more  positive 
electricity  flows  up  into  the  rubbers  from  the  earth  with 
which  they  are  in  connection,  or,  as  we  might  of  course 
say,  the  rubbers  acquire  negative  electricity,  from  friction 
with  the  glass,  and  this  flows  away  into  the  earth;  for,  as 
I have  previously  pointed  out,  all  we  know  is  that  what 
is  called  a flow  of  electricity  is  a flow  of  something  which, 
in  its  motion,  follows  the  laws  of  flow  of  a liquid,  but  which 
way  it  is  flowing  we  do  not  know.  As  the  plate  turns 
round,  the  positive  electricity  is  brought  opposite  to  the 
points,  being  kept  from  escaping  back  to  the  rubbers  by 
means  of  silk  coverings,  which  extend  from  the  rubbers  to 
the  points  in  the  direction  in  which  the  plate  is  turned,  and 
surrounding  its  edge.  The  positive  electricity  on  the  plate, 
as  the  latter  passes  between  the  points,  drives  the  positive 
electricity  of  the  prime  conductor  to  the  further  portion,  and 
therefore  leaves  the  points  and  the  portion  of  the  conductor 
in  their  neighborhood  with  a deficiency  of  positive  electric- 


SOURCES  OF  ELECTRICITY 


45 


ity,  or,  as  we  may  say,  electrifies  them  negatively.  There 
will  therefore  be  a force  acting  upon  the  electricity  on  the 
points,  tending  to  drive  the  negative  electrification  outward 
from  the  points  toward  the  glass,  or,  in  other  words,  tending 
to  draw  positive  electricity  away  from  the  glass  plate  on  to 
the  points  of  the  conductor.  The  portion  of  the  glass  plate 
opposite  the  points  thus  loses  the  greater  portion  of  its 
charge.  In  passing  through  the  second  pair  of  rubbers,  it 
again  becomes  charged  as  before,  and  this  charge  is  deliv- 
ered up  to  the  second  set  of  points.  This  process  continues 
until  the  potential  of  the  conductor  is  so  nearly  equal  to 
that  of  the  plate  that  the  force  between  the  two  becomes 
too  small  to  cause  any  further  transfer  of  electricity.  If, 
however,  some  outlet  is  provided  for  the  electricity  which 
accumulates  upon  the  prime  conductor,  the  action  may  be 
continued  indefinitely,  a stream  of  electricity  being  kept 
flowing  from  the  plate  through  the  prime  conductor  back 
to  the  rubber.  If  the  prime  conductor  is  connected  di- 
rectly with  the  rubber  by  means  of  a wire  or  other  con- 
ductor, the  arrangement  may  be  represented,  according  to 
the  water  analogy  which  I have  previously  used,  by  means 
of  an  endless  tube,  at  one  point  of  which  a pump  is  placed, 
maintaining  a continuous  circulation  of  water  through  the 
tube.  If  the  prime  conductor  and  the  rubber  are  both 
connected  to  the  earth,  the  only  difference  in  the  analogy 
will  be  that  we  must  cut  the  tube  at  a certain  point,  and 
connect  its  two  ends  with  a reservoir  of  water,  when  it  is 
clear  that  the  quantity  of  water  drawn  in  at  one  end  of  the 
tube,  in  a given  interval  of  time,  will  be  exactly  equal 
to  the  quantity  expelled  at  the  other  end. 


46 


ELECTRICITY  IN  MODERN  LIFE 


Influence  Machines 

The  action  of  the  influence  machine  may  be  most  easily 
understood  by  considering  it  in  the  following  simplified 
form.  Suppose  we  have  two  tin  cans,  which  we  will  call 
A and  B,  supported  upon  insulating  stands,  and  let  a small 
charge  of  positive  electricity  be  given  to  the  can  A.  Now, 
suppose  we  have  a brass  ball,  which  I will  call  C,  insulated 
by  being  attached  to  a handle  of  glass  or  ebonite.  Let  the 
ball  C be  held  by  this  insulating  handle  close  to  the  outside 
of  A without  touching  it.  While  in  this  position  let  the 
ball  C be  connected  with  the  earth  by  touching  it  momen- 
tarily with  the  finger.  Now  remove  the  ball  by  its  insulat- 
ing handle,  and  bring  it  into  contact  with  the  inside  of  B, 
near  the  bottom.  The  ball  0,  being  almost  completely  sur- 
rounded by  the  can  B,  will  give  up  its  electrification  almost 
entirely  to  B,  so  that  B will  become  negatively  electrified, 
while  the  ball  will  become  neutral.  Now,  hold  the  ball  0 
outside  and  close  to  the  vessel  B,  and  touch  it  for  a moment 
as  before.  It  will  then  become  positively  charged  by  the 
negative  charge  on  B.  Touch  the  inside  of  A with  it,  near 
the  bottom,  and  it  will  give  up  its  charge  almost  entirely  to 
A,  thus  increasing  the  positive  charge  of  A.  This  increased 
charge  is  then  used  in  the  same  manner  as  the  original  one, 
to  electrify  C negatively,  and  the  charge  on  A being  in- 
creased, the  negative  charge  on  0 will  be  greater  than 
before.  This  is  given  up  to  B just  as  before,  and  the 
increased  negative  charge  of  B is  then  used  to  develop, 
by  induction,  an  increased  positive  charge  on  C,  which  is 
transferred  again  to  A.  Continuing  this  process,  the  dif- 
ference of  potential  between  A and  B may  be  increased  to 
such  an  extent  that  if  they  are  brought  close  together  a 


SOURCES  OF  ELECTRICITY 


47 


spark  will  pass  from  one  to  the  other.  The  influence  ma- 
chine simply  consists  of  an  arrangement  for  carrying  out  a 
similar  series  of  operations  in  rapid  succession.  A revolv- 
ing carrier,  or  series  of  carriers,  is  used,  together  with  an 
inductor,  or  series  of  inductors,  between  which  and  the  car- 
rier a certain  small  difference  of  potential  must  be  excited 
in  order  that  the  machine  may  start.  The  carriers  as  they 
pass  the  inductors  are  electrified  by  induction,  and  when 
passing  out  of  the  sphere  of  influence  of  the  inductor  they 
are  touched  by  a spring  connected  with  a collector,  which 
in  its  turn  acts  as  an  inductor,  and  in  this  way  a very  small 
initial  difference  of  potential  can  be  rapidly  increased  to  a 
considerable  extent.  With  the  older  forms  of  influence 
machines  it  was  necessary  to  begin  by  electrifying  one  of 
the  inductors.  Influence  machines,  however,  are  now  made 
which  are  able  to  excite  themselves  without  external  assist- 
ance by  means  of  the  infinitesimal  difference  of  potential 
which  invariably  exists  between  the  inductors,  and  which 
is  sufficient  to  begin  the  series  of  operations.  The  reader 
may  be  acquainted  with  Clarke’s  electric  gaslighter,  which 
consists,  to  outward  appearance,  of  a flat  disk  some  two  or 
three  inches  in  diameter,  from  opposite  sides  of  the  edge 
of  which  project,  on  one  side  a handle,  and  on  the  other 
a tube  of  any  desired  length,  containing  a pair  of  insulated 
wires,  the  ends  of  which  come  close  together  without  touch- 
ing, just  within  the  further  end  of  the  tube.  To  light  the 
gas  with  the  instrument  the  further  end  of  the  tube  is  held 
in  the  gas  jet,  and  a small  projection  in  the  edge  of  the  disk 
is  pressed  smartly  down,  upon  which  something  is  heard  to 
be  spinning  rapidly  inside  the  disk,  and  sparks  are  seen  to 
pass  between  the  two  wires  just  within  the  end  of  the  tube. 
This  is  simply  a small  influence  machine  of  the  kind  de- 

SCIENCE — VOL.  XTTI — 3 


48 


ELECTRICITY  IN  MODERN  LIFE 


scribed,  the  mechanical  arrangement  being  such  that  on 
pressing  the  button  on  the  edge  of  the  disk  the  revolving 
portion  is  set  in  rapid  motion.  The  Wimshurst  machine, 
so  called  from  the  name  of  its  inventor,  is  another  exam- 
ple of  influence  machines.  It  consists  in  its  simplest  form 
of  a pair  of  glass  disks,  mounted  upon  a common  axle,  close 
together,  but  without  touching  each  other,  in  such  a way 
that  they  can  be  made  to  revolve  rapidly  in  opposite  direc- 
tions. Strips  of  tin-foil  are  pasted  radially  on  the  outside 
surfaces  of  the  glass,  and  metallic  collecting  brushes  are 
made  to  press  against  the  revolving  pieces  of  tin-foil  as  they 
pass  certain  flxed  positions.  Large  machines  of  this  kind  are 
capable  of  imitating  the  effects  of  a thunder-storm  upon  a 
small  scale,  giving  sparks  several  feet  in  length  and  follow- 
ing in  rapid  succession.  In  a dark  room  these  series  of 
sparks  exactly  reproduce  the  appearance  of  forked-lightning 
on  a small  scale.  Small  influence  machines,  soniewhat  simi- 
lar to  those  used  for  gas-lighting,  are  employed  for  igniting 
blasting  charges  in  mines. 

Magneto  and  Dynamo  Machines 

These  machines  all  depend  upon  the  principle  that  elec- 
tric currents  are  induced  in  conductors  which  are  moving 
in  the  neighborhood  of  magnets,  or  more  generally,  which 
are  moving  in  a field  of  magnetic  force,  which  may  be  due 
to  the  presence  of  either  permanent  or  electro-magnets. 
Dynamos  are  now  always  employed  when  powerful  electric 
currents  are  required  for  commercial  purposes,  such  as  for 
electric  lighting  or  electro-plating.  It  is  necessary,  there- 
fore, in  order  to  understand  many  of  the  most  important 
applications  of  electricity  to  commercial  and  domestic  pur- 
poses, to  obtain  something  more  than  a mere  vague,  general 


SOURCES  OF  ELECTRICITY 


49 


idea  of  the  construction  and  action  of  a dynamo;  and  as  the 
subject  must  be  treated  in  some  detail  in  order  to  make  it 
intelligible,  I shall  devote  a separate  chapter  to  it.  I there- 
fore pass  on  to  the  consideration  of 

Galvanic  or  Voltaic  Batteries 

These  are  used  for  the  purposes  of  telegraphy  and  te- 
lephony, and  for  many  others  in  which  only  comparatively 
small  currents  of  electricity  are  required.  A galvanic  or 
voltaic  cell  consists  essentially  of  two  different  metals  im- 
mersed in  some  substance,  generally  a liquid,  composed  of 
two  or  more  chemical  elements,  one  at  least  of  which  tends 
to  combine  with  one  or  other  of  the  two  metals,  or  with  one 
more  than  with  the  other.  When  the  two  metals  are  elec- 
trically connected  outside  the  liquid,  the  circuit  is  said  to  be 
closed;  when  they  are  not  so  connected,  the  circuit  is  said 
to  be  open.  If  the  connecting  wire  is  cut,  its  ends  are  called 
electrodes,  the  free  end  o‘f  the  wire  connected  with  the  plate 
from  which  the  current  is  flowing  through  the  connecting 
wire  being  called  the  positive  electrode,  and  the  free  end  of 
the  other  wire  being  called  the  negative  electrode.  A very 
simple  form  of  cell  consists  of  a plate  of  zinc  and  a plate  of 
copper  partly  immersed  in  sulphuric  acid.  It  will  generally 
be  found,  even  if  there  is  no  electrical  contact  between  the 
zinc  and  copper,  except  through  the  liquid,  that  the  zinc 
will  dissolve  slowly  in  the  acid,  giving  off  bubbles  of  gas 
at  different  parts  of  its  surface;  but  if  the  zinc  and  copper 
are  connected  by  a wire,  the  action  will  be  found  to  increase 
considerably.  The  oxygen  set  free  by  the  decomposition  of 
the  sulphuric  acid  is  given  off  at  the  zinc  plate,  while  the 
hydrogen  is  given  off  at  the  copper  plate.  This  process  is 
effected  in  the  following  manner:  Sulphuric  acid  consists 


50 


ELECTRICITY  IN  MODERN  LIFE 


of  two  atoms  of  hydrogen  in  combination  with  an  atom  of 
sulphur  and  four  atoms  of  oxygen,  and  is  therefore  repre- 
sented by  the  formula  Ha  SO^.  The  molecules  of  acid  are 
continually  being  broken  up,  chiefly,  there  is  reason  to 
believe,  into  the  groups  Ha,  and  SO4.  When  the  electrical 
potential  of  the  liquid  is  the  same  throughout  these  groups 
recombine,  as  fast  as  they  are  broken  up,  to  form  fresh 
molecules  of  Ha  SO4;  but  when  a difference  of  potential 
is  maintained  between  different  portions  of  the  liquid,  the 
molecules  of  hydrogen  move  from  places  of  higher  to  places 
of  lower  potential,  just  as  if  they  carried  a positive  charge 
of  electricity;  while  the  groups  of  SO*  travel  in  the  oppo- 
site direction,  as  though  their  electrification  were  negative. 
Thus,  though  the  two  constituents  continually  form  fresh 
molecules  during  the  journey,  only  to  be  again  broken  up, 
there  is,  on  the  whole,  a continual  flow  of  hydrogen  in  one 
direction,  and  of  SO4  in  the  other.  The  hydrogen  is  given 
off  at  the  copper  plate;  while  the  SO^,  on  arriving  at  the 
zinc  plate,  where  there  is  no  free  hydrogen  to  combine  with 
it,  takes  the  hydrogen  from  a molecule  of  water  (HaO),  and 
leaves  the  oxygen  free.  The  chemical  action  which  goes  on 
before  the  circuit  is  closed  contributes  nothing  toward  the 
current  of  electricity,  and  is  known  as  local  action.  It  is 
caused  chiefly  by  impurities  in  the  zinc,  and  may  be  almost 
entirely  obviated  by  amalgamating  the  zinc  with  mercury. 

The  manner  in  which  the  B.M.F.  is  produced  in  a 
galvanic  cell  is  still  an  open  question  among  electricians, 
but  the  consideration  of  the  following  experimental  facts 
will  help  the  reader  to  attain  a general  understanding  of  the 
action  of  a cell: 

(1)  If  a piece  of  copper  is  placed  in  contact  with  a piece 
of  zinc  a difference  of  potential  will  be  produced  at  the 


SOURCES  OF,  ELECTRICITY 


51 


point  of  contact,  the  zinc  becoming  positively  electrified 
and  the  copper  negatively,  so  that  the  potential  of  the  zinc 
is  higher  than  that  of  the  copper.  The  charges  so  produced 
are  always  very  small. 

(2)  If  either  the  copper  or  zinc  is  immersed  alone  in  the 
dilute  sulphuric  acid  a difference  of  potential  will  be  produced 
between  the  metal  and  the  liquid;  but  if  the  two  metals  are 
immersed  side  by  side  into  the  liquid  then  no  electrifica- 
tion can  be  detected,  so  that  all  three  must  be  at  the  same 
potential. 

(3)  If  a piece  of  copper  is  now  joined  to  the  zinc,  the 
copper,  being  in  contact  with  the  zinc,  will  become  nega- 
tive, and  the  zinc  positive,  while  the  liquid  and  the  copper 
immersed  in  it  will  stil]  have  the  same  potential  as  the  zinc 
— that  is,  they  will  be  positive.  Now,  suppose  the  piece  of 
copper  attached  to  the  zinc  to  be  bent  round  and  connected 
with  the  copper  plate  of  the  cell,  then  the  action  of  the  liquid 
is  continually  to  do  away  with  the  difference  of  potential 
caused  by  the  contact  of  copper  and  zinc,  and  this  requires 
a flow  of  electricity  from  zinc  to  copper  within  the  liquid, 
and  therefore  from  copper  to  zinc  in  the  connecting  wire. 

When  a series  of  galvanic  cells  is  so  arranged  that  the 
zinc  of  each  cell  is  connected  with  the  copper  of  the  next 
cell,  the  arrangement  is  called  a galvanic  battery,  or  voltaic 
battery.  If  each  cell  is  made  of  similar  materials,  the  differ- 
ence of  potential,  or  electro-motive  force,  of  the  battery  will 
be  equal  to  the  product  of  the  electro-motive  force  of  one 
cell  by  the  number  of  cells. 

If  a cell  of  the  simple  kind  already  described  is  em- 
ployed, or  a battery  of  such  cells,  for  producing  an  electric 
current,  after  a short  time  a number  of  small  bubbles  of  gas 
will  be  observed  to  be  adhering  to  the  copper  plates  within 


52 


ELECTRICITY  IN  MODERN  LIFE 


the  liquid,  and  at  the  same  time  it  will  be  found  that  the 
B.M.F.  of  the  battery  has  become  very  much  less  than  it 
was  at  first.  It  can  be  shown  that  this  is  due  to  an  E.M.F. 
opposite  in  direction  to  that  of  the  battery  being  set  up 
between  the  bubbles  and  the  copper. 

This  phenomenon  is  known  by  the  name  of  polarization, 
and  the  B.M.F.  due  to  it  is  called  the  E.M.F.  of  polariza- 
tion. The  polarization  of  a cell  may  be  diminished  by  any 
means  which  will  cause  the  bubbles  to  rise  to  the  surface 
instead  of  remaining  adhering  to  the  copper — as,  for  exam- 
ple, by  stirring  the  liquid,  or  by  blowing  air  through  it.  If 
the  surface  of  the  copper  is  roughened  the  gas  will  collect 
chiefly  at  the  projecting  portions,  and  therefore  the  bubbles 
will  attain  a size  sufficient  to  rise  to  the  surface  much  sooner 
than  if  the  surface  were  smooth.  With  the  object  of  obtain- 
ing a rough  surface  of  this  kind,  Smee  devised  a cell  which 
differed  from  the  typical  form  described  only  in  the  fact 
that  the  plates  of  copper  were  replaced  by  plates  of  silver 
covered  with  a coat  of  platinum  in  a very  fine  state  of  divi- 
sion. These  plates  give  off  the  bubbles  very  freely,  but 
still  the  remedy  is  only  a partial  one,  and  the  E.M.F.  of  the 
battery  is  found  to  fall  considerably  after  it  has  been  in 
action  for  a few  minutes. 

A much  more  efficient  means  of  overcoming  polarization 
is  to  employ,  as  the  liquid  surrounding  the  plate  at  which 
hydrogen  is  set  free,  a solution  containing  some  highly 
oxidizing  substance.  The  hydrogen  as  it  is  set  free  will 
then,  instead  of  forming  into  bubbles,  unite  with  the  oxygen 
of  this  substance  to  form  water.  These  substances,  however, 
cannot  be  employed  in  a zinc  copper  cell,  as  the  copper 
would  be  dissolved  in  them,  and  some  of  them  would  also 
attack  the  zinc  as  soon  as  the  circuit  was  broken.  This 


SOURCES  OF  ELECTRICITY 


53 


difficulty  was  overcome  by  PoggendorS,  who  devised  the 
“Bichromate”  cell,  consisting  of  plates  of  carbon  and  zinc 
immersed  in  a solution  of  bichromate  of  potash,  to  which 
a small  quantity  of  sulphuric  acid  has  been  added.  This 
solution  begins  to  dissolve  the  zinc  as  soon  as  the  circuit  is 
broken,  and  therefore  arrangements  have  to  be  made  for 
lifting  the  zinc  out  of  the  solution.  Nitric  acid  is  a highly 
oxidizing  substance,  and  very  suitable  as  a liquid  in  which 
to  immerse  the  positive  plate;  but  it  will  not  do  to  have  the 
zinc  immersed  in  nitric  acid,  as  the  action  of  the  acid  on 
the  zinc  as  soon  as  the  circuit  is  broken  would  be  exceed- 
ingly rapid.  Bunsen  therefore  devised  a cell,  in  which  the 
positive  plate  is  formed  of  carbon  immersed  in  strong  nitric 
acid.  The  acid  is  placed  in  a porous  pot,  and  this  porous 
pot  is  itself  placed  in  a vessel  containing  a zinc  plate  and 
dilute  sulphuric  acid.  The  porous  pot  allows  the  liquid  to 
pass  into  its  pores,  so  that  the  products  of  the  chemical 
decomposition  going  on  in  the  cell  can  pass  through  it  under 
the  influence  of  E.M.F. ; but  if  the  liquids  inside  and  outside 
the  porous  cell  respectively  are  at  the  same  level,  ordinary 
mixture  of  the  liquids  will  only  take  place  exceedingly 
slowly.  The  Bunsen  cell  is  a very  good  one  where  a strong 
current  is  required,  but  it  is  necessary  after  using  it  to  soak 
the  carbons  for  some  hours  in  water  to  get  rid  of  the  nitric 
acid  which  they  have  absorbed.  In  a cell  devised  by  Mr. 
Justice  Grove,  and  therefore  known  as  the  Grove  cell,  the 
carbon  is  replaced  by  a sheet  of  platinum,  which  can  be 
washed  much  more  easily.  After  using  either  of  these  cells 
the  solutions  must  be  poured  out,  as  otherwise  gradual  mix- 
ture of  the  two  will  take  place.  Neither  of  them  is  pleasant 
to  use  in  a room,  as  they  give  off  an  exceedingly  pungent 
gas  known  as  nitrous  oxide. 


54 


ELECTRICITY  IN  MODERN  LIFE 


The  polarization  difficulty  has  been  overcome  in  another 
way  in  the  Daniell  cell,  which  consists  of  a zinc  rod  or  plate 
immersed  in  sulphuric  acid,  and  a copper  plate  immersed  in 
a saturated  solution  of  sulphate  of  copper.  The  solutions 
are  separated  by  a porous  division,  one  of  them  being 
usually  contained  in  a porous  pot  immersed  in  the  other. 
In  this  cell  the  hydrogen,  set  free  as  the  zinc  dissolves  in 
the  acid,  passes  through  the  porous  division  into  the  solu- 
tion of  sulphate  of  copper,  which  it  decomposes,  forming 
sulphuric  acid,  and  depositing  a layer  of  copper  upon  the 
copper  plate.  The  strength  of  the  solution  is  kept  up  by 
placing  some  crystals  of  the  salt  in  it,  which  dissolve  as  fast 
as  the  copper  is  deposited,  so  that  the  solution  of  sulphate  of 
copper  is  maintained  at  the  point  of  saturation. 

Another  battery  which  must  be  mentioned,  as  it  is  exten- 
sively used  for  telegraphic  and  telephonic  purposes,  and  also 
for  ringing  electric  bells,  is  the  Leclanche  cell.  This  cell 
consists  of  a vessel  containing  a solution  of  salammoniac, 
in  which  are  immersed  a zinc  rod  or  plate,  and  a porous  pot 
packed  with  lumps  of  carbon  and  powdered  binoxide  of 
manganese.  The  zinc  dissolves  in  the  salammoniac,  and 
bubbles  of  hydrogen  are  formed  on  the  carbon  plate ; so  that 
if  the  circuit  is  kept  closed  for  any  length  of  time,  the 
E.M.F.  will  be  found  to  fall  considerably.  This  afiords 
an  explanation  of  a fact  which  may  probably  have  been 
noticed  by  many  of  my  readers,  that  an  electric  bell,  worked, 
as  is  usually  the  case,  by  means  of  one  or  more  of  these 
cells,  will  soon  cease  ringing  if  the  button  is  kept  pressed 
down,  and  will  sometimes  fail  to  act  if  it  has  been  rung  a 
good  many  times  in  rapid  succession.  When  the  battery 
is  left  to  itself  for  a short  time  the  oxygen  from  the  oxide  of 
manganese  gradually  combines  with  the  hydrogen  bubbles 


SOURCES  OF  ELECTRICITY 


55 


to  form  water,  and  in  this  way  the  B.M.F.  of  the  battery  is 
restored  to  its  original  value. 

Batteries  like  the  Grrove  or  the  Bunsen  are  very  suitable 
for  maintaining  an  electric  light  for  an  hour  or  two  for 
experimental  purposes,  and  a bichromate  battery  will  do 
very  well  for  the  same  purpose  if  the  light  is  only  required 
for  a still  shorter  time — as,  for  example,  to  supply  current 
for  a lamp  to  stand  at  the  bedside  to  observe  the  time  by 
the  clock  during  the  night — the  battery  being  brought  into 
action  when  required  by  pressing  down  a rod  which  im- 
merses the  zinc  in  the  solution,  a spring  lifting  it  again  as 
soon  as  the  pressure  is  removed.  Small  incandescent  lamps 
supplied  with  current  from  a bichromate  cell  are  often  sold 
as  reading  lamps,  but  after  burning  from  half  an  hour  to  two 
or  three  hours,  according  to  the  size  of  the  cell,  they  will 
gradually  become  dim  and  ultimately  cease  to  glow  alto- 
gether, when  the  battery  must  be  refilled  with  fresh  solution. 
It  is  impossible  commercially  to  supply  the  electric  light  by 
means  of  any  form  of  galvanic  battery,  or  primary  battery, 
at  present  known  to  us,  for  the  simple  reason  that  in  these 
batteries  the  energy  is  obtained  from  the  consumption  of 
zinc  or  other  material,  which  costs  many  times  more  than 
coal.  The  object  in  using  a dynamo  instead  of  a battery  to 
supply  the  current  is,  that  instead  of  having  to  burn  an 
expensive  fuel,  such  as  zinc,  to  obtain  energy,  it  can  be 
obtained  by  burning  the  cheaper  fuel,  coal;  and  though 
a considerable  amount  of  the  energy  obtained  from  the  coal 
is  lost,  first  in  the  process  of  transforming  heat  into  mechani- 
cal work  in  the  steam  engine,  and  secondly  in  the  transfor- 
mation of  mechanical  into  electrical  energy  in  the  dynamo, 
still  the  difference  between  the  cost  of  coal  and  that  of  zinc 
is  so  great  that  the  cost  of  producing  electricity  on  a large 


56 


ELECTRICITY  IN  MODERN  LIFE 


scale  by  means  of  a dynamo  is  many  times  less  than  it  would 
be  if  any  form  of  primary  battery  were  used. 


CHAPTER  VI 

MAGNETIC  FIELDS 

AS  there  will  be  frequent  occasion  in  this  and  the  fol- 
lowing chapters  to  make  use  of  the  term  “Magnetic 
Field,”  it  will  be  important  for  the  reader  to  obtain 
an  exact  conception  of  its  meaning. 

A Magnetic  Field  may  be  defined  as  a region  within 
which  magnetic  force  acts — that  is  to  say,  it  is  a region 
of  such  a kind  that  if  a magnet  is  introduced  into  it,  it  will 
be  subject  to  the  action  of  certain  forces  in  virtue  of  its  mag- 
netism; and  if  a magnetic  substance  is  introduced  into  such 
a region  it  will  become  magnetized — that  is  to  say,  it  will 
acquire  magnetic  properties.  A clearer  idea  of  what  is 
meant  by  a magnetic  field,  or  a field  of  magnetic  force,  will 
perhaps  be  obtained  by  supplementing  this  definition  by  the 
consideration  of  some  field  of  force  of  a more  familiar  char- 
acter than  magnetic  force.  Consider,  for  example,  what 
happens  when  a comet  is  moving  through  space  in  the 
neighborhood  of  the  solar  system. 

The  comet  would  be  attracted  by  the  sun,  and  if  it  were 
originally  at  rest,  and  the  sun  were  the  only  other  body  in 
the  universe,  the  comet  would  be  drawn  directly  toward  it, 
and  the  force  tending  to  draw  the  two  bodies  together  would 
increase,  as  they  approached  each  other,  at  such  a rate  that 
when  the  distance  between  the  sun  and  the  comet  was 
halved  the  force  would  amount  to  four  times  its  original 


MAGNETIC  FIELDS 


57 


value;  when  the  distance  was  diminished  to  one-third  of  its 
original  amount,  the  force  of  attraction  would  be  nine  times 
as  great  as  at  first;  when  the  distance  was  diminished  to 
one-fourth,  the  attraction  would  be  sixteen  times  as  great, 
and  so  on.  In  other  words,  the  attraction  between  the  two 
bodies  would  be  inversely  proportional  to  the  square  of 
the  distance  between  them.  Considering  then  merely  the 
motion  of  the  comet  in  obedience  to  the  force  acting  upon 
it,  it  may  be  regarded  as  moving  in  a field  of  force  of  such 
a character  that  the  intensity  of  the  force  is  the  same  at  all 
points  of  any  spherical  surface  described  with  the  centre 
of  the  sun  as  its  centre,  while  the  direction  of  the  force  is 
always  along  the  radius.  This  field  of  force  may  be  mapped 
out  in  such  a way  as  to  exhibit  at  a glance  the  magnitude 
and  direction  of  the  force  exerted  upon  the  comet  at  any 
point. 

Describe  a number  of  spherical  surfaces,  each  having  the 
sun  as  centre,  and  therefore  lying  one  within  the  other,  and 
let  the  distance  between  any  sphere  and  the  one  immediately 
outside  it  be  calculated  from  the  law  of  attraction  in  such 
a way  that  the  force  always  diminishes  by  the  same  amount 
in  passing  from  any  one  sphere  to  the  next  outside  it. 

If  these  spheres  are  drawn  close  enough,  the  whole  region 
will  then  be  mapped  out  in  such  a way  that  the  ratio  of  the 
rate  of  change  of  the  force  acting  on  the  comet  at  any  point 
of  its  path,  to  that  at  any  other  point,  will  be  the  same  as 
the  ratio  of  the  distance  between  the  two  adjacent  spheres 
inclosing  the  first  point,  to  the  distance  between  the  two 
adjacent  spheres  which  inclose  the  second  point. 

The  direction  of  the  force  at  any  point  will  be  along  the 
line  joining  that  point  to  the  common  centre  of  the  spheres, 
that  is  to  the  centre  of  the  sun,  and  it  will  therefore  always 


58 


ELECTRICITY  IN  MODERN  LIFE 


be  perpendicular  to  the  surface  of  the  sphere  passing  through 
the  point.  Such  a line,  which  represents  the  direction  ot 
the  force  acting  on  the  comet  at  any  point,  is  called  a line 
of  force;  and  each  sphere,  being  a surface  everywhere 
perpendicular  to  the  direction  of  the  force,  is  called  a level 
surface. 

It  is  clear  that  in  the  present  case  the  distance  between 
two  adjacent  spherical  surfaces,  at  such  a small  distance 
apart  relatively  to  their  distance  from  the  common  centre 
that  the  difference  between  these  distances  may  be  neglected, 
will  be  inversely  proportional  to  their  common  distance  from 
the  centre  of  the  field  of  force.  The  field  will  therefore  be 
completely  defined  by  the  statements — 

(1)  That  the  level  surfaces  are  spheres  with  the  centre  of 
the  sun  as  their  common  centre. 

(2)  That  the  distance  between  any  two  adjacent  spheres 
is  inversely  proportional  to  the  distance  of  their  surfaces 
from  the  centre. 

It  will  be  convenient,  for  the  purpose  of  applying  these 
considerations  to  magnetic  fields,  to  define  the  fields  by 
means  of  what  are  called  unit  tubes  of  force  instead  of 
by  the  level  surfaces. 

Imagine  a small  closed  curve  to  be  drawn  on  one  of  the 
spheres,  and  let  the  force  across  the  small  area  inclosed  by 
the  curve  be  taken  as  the  unit  of  force,  then  all  the  lines 
of  force  passing  through  the  boundary  of  this  small  area  will 
form  a tube,  which  is  called  a unit  tube  of  force.  In  the 
case  of  the  field  of  gravitation  force  due  to  the  sun,  these 
tubes  will  clearly  be  cones  having  their  vertices  at  the  centre 
of  the  sun,  and  it  could  easily  be  shown  mathematically 
that  the  force  of  attraction  on  a unit  mass  placed  anywhere 
in  the  field  of  force  would  be  inversely  proportional  to  the 


MAGNETIC  FIELDS 


59 


area  of  the  section  of  the  tube  made  by  the  level  surface 
through  the  point. 

Any  portion  of  the  field  of  force  will  thus  be  fully  defined 
by  the  unit  tubes  of  force  drawn  in  this  manner,  for  the 
direction  of  the  line  of  force  at  any  point  gives  the  direction 
of  the  force,  while  the  number  of  unit  tubes  passing  through 
unit  area  on  the  level  surface  through  the  point  may  be 
taken  as  a measure  of  the  intensity  of  the  force.  So  far  the 
comet  has  been  supposed  to  be  acted  on  only  by  the  force 
of  attraction  of  the  sun.  This,  however,  is  not  really  the 
case,  for  every  planet  and  satellite  of  the  solar  system  is  at 
the  same  time  attracting  the  comet  toward  itself  with  a force 
proportional  to  its  mass,  and  inversely  proportional  to  the 
square  of  its  distance  from  the  comet. 

Now,  according  to  the  experimentally  observed  laws  of 
motion  discovered  and  enunciated  by  Sir  Isaac  Newton,  the 
force  exerted  by  each  body  is  independent  of  the  forces 
exerted  by  the  others,  and  therefore  it  becomes  a mere 
question  of  mathematical  calculation  to  map  out  the  field 
of  force  in  which  the  comet  is  actually  moving. 

Such  a field  may,  as  before,  be  defined  by  means  of  its 
level  surfaces,  or  by  means  of  its  unit  tubes  of  force;  but 
the  level  surfaces  will  no  longer  be  spheres,  and  the  lines  of 
force  will  no  longer  be  straight  lines.  Now,  just  as  the  field 
of  force  in  which  the  comet  is  moving  has  been  mapped  out, 
so  we  may  map  out  a field  of  magnetic  force ; and  it  was  first 
in  connection  with  the  mapping  out  of  magnetic  fields  that 
Faraday  introduced  the  idea  of  lines  of  force,  and  the 
method  of  mapping  out  a field  of  force  by  their  means.  It 
seemed,  however,  to  me  that  it  would  be  easier  to  approach 
the  subject  through  the  better  known  case  of  gravitation 
force. 


60 


ELECTRICITY  IN  MODERN  LIFE 


A very  simple  means  of  studying  magnetic  fields  experi- 
mentally is  to  place  a sheet  of  stiff  paper  or  cardboard  in  the 
portion  of  the  field  in  which  we  wish  to  know  the  distribu- 
tion of  magnetic  force,  and  to  dust  it  over  with  iron  filings, 
when  the  filings  will  arrange  themselves  along  the  lines  of 
force.  It  will  be  of  interest  to  illustrate  this  by  considering 
a few  simple  cases. 

Let  the  magnetic  field  be  that  due  to  a single  magnetic 


Fig.  1. 


pole.  This  may  be  practically  obtained  by  holding  a long 
narrow  bar  magnet  vertically  under  the  cardboard,  with  one 
end  in  contact  with  its  under  surface,  and  then  dusting  the 
filings  upon  the  upper  surface,  tapping  the  card  slightly 
during  the  process.  The  further  pole  of  the  magnet  will  be 
so  far  from  the  card  that  it  will  not  produce  any  sensible 
effect,  so  that  the  field  will  be  practically  that  due  to  the 
nearest  pole. 


MAGNETIC  FIELDS 


61 


The  filings  will  then  arrange  themselves  in  a series  of 
lines  radiating  from  a common  centre  immediately  over 
the  pole  of  the  magnet  in  contact  with  the  cardboard,  as 
shown  in  Fig.  1.  In  this  way,  of  course,  we  only  obtain  a 
representation  of  a section  of  the  field  of  force.  If  we  could 
obtain  a single  separate  magnetic  pole — which,  as  a matter 
of  fact,  is  impossible — the  magnetic  field  surrounding  it 


Fig.  2. 


would  be  of  a character  exactly  similar  to  the  field  of  force 
surrounding  a sphere  of  gravitating  matter,  as  in  the  case 
of  the  sun  previously  considered. 

If  the  bar  magnet  is  held  horizontally  under  the  card- 
board so  as  to  touch  along  its  whole  length,  the  filings  will 
arrange  themselves  as  shown  in  Fig.  2,  which  there  repre- 
sents a section,  through  the  line  joining  the  poles,  of  the 
field  of  force  due  to  a pair  of  opposite  poles. 


62 


ELECTRICITY  IN  MODERN  LIFE 


The  actual  form  of  the  lines  of  force  in  the  space  sur- 
rounding the  poles  of  a magnetized  bar  is  shown  in  Fig.  3. 

The  field  of  force  sur- 
rounding an  electric  current 
may  be  exhibited  in  a simi- 
lar manner.  Thus  bore  a 
hole  through  a piece  of 
cardboard,  and  pass  a wire 
which  carries  a current  up  through  the  hole,  allowing  it  to 
stand  at  right  angles  to  the  card.  The  iron  filings  will 
then  arrange  themselves  in  a series  of  circles,  having  this 
hole  as  their  common  centre,  as  shown  in  Fig.  4.  The  level 


Fig  4. 


-surfaces,  being  perpendicular  to  the  lines  of  force,  evi- 
dently consist,  in  this  case,  of  a series  of  planes  passing 
through  the  straight  wire. 

In  the  case  of  the  field  of  gravitation  force  in  which 


MAGNETIC  FIELDS 


63 


a comet  was  moving,  considered  at  the  beginning  of  the 
chapter,  the  direction  of  the  force  at  any  point  would  be 
that  in  which  the  comet  would  move  if  it  were  placed  at  that 
point  without  any  motion  being  given  to  it  other  than 
that  due  to  the  gravitation  force. 

In  the  case  of  a magnetic  field,  a north  pole  and  a south 
pole  tend  to  move  in  opposite  directions  along  a line  of  force, 
and  we  select  as  the  positive  direction  of  a line  of  force,  or 
the  direction  of  the  magnetic  force  at  a point,  that  direction 
in  which  a north  pole  would  move  if  unconstrained.  The 
reason  that  the  iron  filings  arrange  themselves  along  the 
lines  of  force  is  that  they  become  magnetized  with  their  axes 
in  the  direction  of  their  greatest  length,  and  equal  and 
opposite  forces  acting  upon  their  opposite  poles  set  them 
along  the  lines  of  force;  just  as  when  two  strings  are  tied 
to  the  end  of  a stick  and  pulled  in  opposite  directions  the 
stick  will  set  itself  in  a straight  line  with  the  pair  of  strings. 

It  is  evident,  from  inspection  of  Fig.  4,  that  if  one  of 
the  poles  of  the  magnet  could  be  separated  from  the  other, 
it  might  be  made  to  rotate  continuously  round  a wire  carry- 
ing an  electric  current;  and  though  -it  is  impossible  to  do 
this,  the  truth  of  the  statement  can,  notwithstanding,  be 
demonstrated  in  several  ways. 

Perhaps  the  simplest  of  these  is  to  place  a magnet, 
formed  out  of  a long,  thin,  flexible  steel  wire,  parallel 
and  close  to  a wire  carrying  a current,  when  it  will  be  found 
that  the  two  poles  will  rotate  round  the  wire  in  opposite 
directions,  twisting  the  magnet  round  the  wire. 

It  is  clear,  then,  that  an  electric  current  is  surrounded  by 
a series  of  what  may  be  called  ‘‘magnetic  whirls,”  and  there- 
fore it  becomes  easier  to  see  the  possibility  of  an  electric 
current  being  set  up  in  a wire  moved  across  the  lines  of 


64 


ELECTRICITY  IN  MODERN  LIFE 


force  of  a magnetic  field,  as  Faraday  found  to  be  the  case. 
For  both  magnets  and  conductors  carrying  currents  give  rise 
to  actions  going  on  in  the  medium  surrounding  them  of  such 
a kind  as  might  be  imagined  to  arise  from  a rotation  of  por- 
tions of  the  medium;  and  therefore  when  a wire  is  moved 
across  the  lines  of  force  magnetic  whirls  are  set  up  round 
the  wire,  involving  the  existence  of  what  is  called  a current 
of  electricity. 

Faraday  found  that  the  E.M.F.  excited  in  a conductor 
by  moving  it  across  the  lines  of  force  was  in  the  direction  at 
right  angles  to  that  of  the  motion  and  to  the  direction  of  the 
lines  of  force,  and  the  direction  of  its  action  was  given 
by  the  rule  that  if  we  suppose  a man  swimming  in  the  con- 
ductor to  turn  so  as  to  look  along  the  line  of  force  in  the 
positive  direction,  while  the  conductor  moves  toward  his 
right  hand,  he  will  be  swimming  with  the  current  induced 
by  the  motion.  The  amount  of  the  E.M.F.  Faraday 
found  to  be  proportional  to  the  number  of  unit  tubes 
of  force  cut  per  second,  and  therefore  proportional  to 
the  intensity  of  the  field  and  to  the  length  and  velocity 
of  the  conductor. 

From  what  has  just  been  stated  as  to  the  direction  of 
the  E.M.F.  excited  in  a conductor  when  it  mov^s  across  the 
lines  of  force,  it  follows  that  if  a closed  circuit,  such  as  a 
circle  of  wire,  be  moved  across  them,  the  passage  of  a unit 
tube  of  force  from  the  inside  to  the  outside  of  the  area  in- 
closed by  the  circuit  will  produce  an  E.M.F.  equal  and 
opposite  to  that  due  to  the  passage  of  a unit  tube  from  the 
outside  to  the  inside.  The  current  round  the  circle  will 
therefore  be  proportional  to  the  rate  of  increase  or  decrease 
in  the  number  of  unit  tubes  enveloped  by  the  circuit. 

Instead  of  moving  a conducting  circuit  in  a magnetic  field 


MAGNETIC  FIELDS 


65 


in  such  a manner  as  to  vary  the  number  of  tubes  of  force 
enveloped  by  it,  this  variation  may  be  effected  by  varying 
the  magnetic  field  while  the  conductor  remains  stationary. 
Thus  if  a magnetic  field  is  made  to  grow  around  a straight 
wire  forming  a portion  of  a conducting  circuit,  by  starting 
a current  in  a second  circuit,  part  of  which  is  parallel  and 
close  to  the  straight  wire,  it  will  give  rise  to  an  induced 
current  in  the  latter  in  the  opposite  direction  to  that  of  the 
inducing  current,  and  continuing  as  long  as  the  inducing 
current  continues  to  increase — that  is  to  say,  as  long  as  the 
magnetic  field  continues  to  grow.  When  the  inducing  cur- 
rent assumes  a steady  value  the  variation  in  the  magnetic 
field,  and  therefore  also  the  induced  current,  will  cease. 
If  the  inducing  current  is  now  allowed  to  die  away  the 
magnetic  field  will  also  begin  to  die  away,  giving  rise  to  an 
induced  current  in  the  straight  wire  in  an  opposite  direction 
to  that  of  the  former  one,  and  lasting  until  the  inducing 
current  has  completely  ceased. 

If  a current  is  suddenly  started  in  a straight  wire  a mag- 
. netic  field  will  be  made  to  grow  round  it,  and  will  give  rise 
to  an  E.M.F.  opposed  to  that  of  the  inducing  current,  the 
effect  of  which  is  to  retard  the  increase  of  the  primary 
current.  If  the  primary  current  is  allowed  to  die  away,  the 
resulting  variation  in  the  magnetic  field  will  give  rise  to  an 
E.M.F.  in  the  direction  of  the  primary  current,  the  effect 
of  which  will  be  to  make  the  current  die  away  more  slowly 
than  it  otherwise  would.  This  phenomenon  is  known  as 
self-induction.  It  is  easy  to  see  that  the  self-induction 
of  a straight  wire  of  given  dimensions  would  be  greatly 
increased  if  it  were  wound  into  a coil,  as  this  would  bring 
the  different  parts  of  the  circuit  much  closer  together,  and 
would  therefore  greatly  increase  the  mutual  induction  of  the 


66 


ELECTRICITY  IN  MODERN  LIFE 


diJfferent  portions — that  is  to  say,  it  would  increase  the  self- 
induction  of  the  circuit. 

It  is  possible  to  arrange  a series  of  magnets  in  such  a 
manner  as  to  make  a magnetic  field  within  a certain  portion 
of  which  the  magnetic  force  is  everywhere  equal  and  in  the 
same  direction.  When  this  is  the  case  the  magnetic  field 
is  said  to  be  uniform,  and  the  lines  of  force  are  all  parallel, 
and  the  section  of  a unit  tube  by  a level  surface  is  the  same 
at  every  point.  If  any  closed  circuit  is  moved  parallel  to  itself 
across  the  field,  the  number  of  unit  tubes  enveloped  by  the 
circuit  will  therefore  remain  unchanged,  so  that  no  current 
will  be  produced;  but  if  the  circuit  is  made  to  rotate,  the 
number  of  unit  tubes  enveloped  will  vary,  and  therefore 
currents  will  be  induced  in  it  during  the  motion. 

Suppose,  to  take  as  simple  a case  as  possible,  that  the 
circuit  consists  simply  of  a circle  of  wire.  In  order  to  fix 
the  ideas,  suppose  that  the  lines  of  force  are  horizontal, 
and  that  the  positive  direction — that  is  to  say,  the  direction 
of  the  magnetic  force — is  from  left  to  right.  Let  the  circle 
be  capable  of  rotation  about  a horizontal  axis  passing 
through  its  centre,  and  perpendicular  to  the  lines  of  force. 
Let  the  circle  be  made  to  turn  about  this  axis  in  the  direc- 
tion of  the  hands  of  a watch,  and  consider  what  happens, 
starting  with  the  circle  in  a horizontal  position.  In  order 
to  define  the  direction  of  the  current  round  the  circle,  sup- 
pose a watch  to  be  placed  in  it  with  its  face  in  its  plane, 
and  directed  toward  the  observer  in  the  initial  position. 
Applying  Faraday’s  rule,  it  is  then  easily  seen  that  during 
the  first  and  last  quarter  revolutions  the  current  round  the 
circle  will  be  in  the  opposite  direction  to  the  motion  of 
the  hands  of  the  watch,  and  in  the  same  direction  as  that 
of  the  hands  during  the  second  and  third  quarter  revolu- 


MAGNETIC  FIELDS 


67 


tions.  The  reversal  of  the  current  will  therefore  take  place 
each  time  that  the  plane  of  the  circle  passes  through  the 
position  of  parallelism  with  the  lines  of  force. 

If,  then,  the  circle  is  made  to  spin  about  a horizontal 
axis,  it  will  be  traversed  by  a series  of  currents  alternately 
in  opposite  directions,  the  change  in  direction  taking  place 
at  each  half  revolution. 

An  approximately  uniform  field  mayi  be  produced  be- 
tween the  poles  of  a magnet  having  its  ends  hollowed  out 
to  a suitable  shape,  and  bent  round  so  as  to  bring  them 
close  together. 

A conductor  such  as  has  been  described,  but  having  its 
ends  cut  at  a point  on  the  axis  of  rotation,  and  connected 
with  conducting  wires  to  carry  the  currents  produced 
wherever  they  are  wanted,  and  arranged  in  such  a manner 
as  to  be  capable  of  rotating  between  the  poles  of  a magnet, 
is  nothing  more  nor  less  than  a dynamo  in  its  simplest 
ideal  form. 

For  some  purposes — as,  for  example,  for  producing  the 
electric  light — the  currents  may  either  flow  alternately  in 
opposite  directions  or  continuously  in  the  same  direction. 
For  other  purposes,  however — such,  for  example,  as  electro- 
plating— it  is  necessary  to  have  the  current  always  in  the 
same  direction  through  the  conducting  wires  or  leads, 
as  they  are  often  called,  and  in  that  case  it  is  necessary 
to  make  use  of  some  kind  of  arrangement  which  reverses 
the  connections  between  the  rotating  conductor  and  the 
leads  whenever  the  direction  of  the  current  in  the  rotating 
portion  is  reversed — that  is  to  say,  at  every  half  revolution. 
An  arrangement  of  this  kind  is  called  a commutator. 

Professor  Sylvanus  P.  Thompson,  in  his  work  on  ‘‘Dy- 
namo-Electric Machinery,’^  from  which,  by  the  kind  per- 


68 


ELECTRICITY  IN  MODERN  LIFE 


mission  of  the  author  and  publisher,  the  illustrations  in  this 
and  the  following  chapter  have  been  taken,  sums  up  the 
guiding  principles  which  have  to  be  borne  in  mind  in  con- 
structing a dynamo,  as  follows — (1)  The  field  magnets 
should  be  as  strong  as  possible,  and  their  poles  as  near  to 
the  armature  as  possible;  (2)  the  armature  should  have  the 
greatest  possible  length  of  wire  upon  its  coils;  (3)  the  wires 
of  the  armature  coils  should  be  as  thick  as  possible,  so  as  to 
offer  little  resistance  to  the  induced  currents;  (4)  the  speed 
of  rotation  should  be  as  great  as  possible. 

These  are  by  no  means  the  only  conditions  which  have 
to  be  considered  in  designing  a satisfactory  dynamo;  but 
even  when  nothing  further  is  taken  into  account,  a system 
of  give  and  take  has  to  be  adopted,  as  it  is  impossible  to 
carry  out  each  of  these  conditions  to  the  fullest  possible 
extent  in  the  same  machine,  and  therefore  it  is  necessary 
to  effect  such  a compromise  as  will  give  the  best  result  for 
the  purpose  in  view. 


ELECTRICAL  MEASUREMENT 


69 


CHAPTER  YII 

ELECTRICAL  MEASUREMENT 

SO  LONG  as  electricity  remained  merely  a laboratory 
science  very  little  attention  was  paid  to  electrical 
measurement,  outside  the  small  circle  of  great  mathe- 
matical electricians  who  were  engaged  in  studying  electrical 
phenomena,  and  investigating  the  general  laws  to  which 
they  were  subject,  from  a purely  scientific  point  of  view. 

For  a long  time  after  electricity  had  become  more  or 
less  a subject  of  general  interest,  the  attention  of  by  far  the 
greater  number,  even  of  those  who  were  engaged  in  teach- 
ing the  subject,  was  mainly  confined  to  the  description  of 
phenomena  without  regard  to  their  quantitative  relations. 

Text- books  of  not  many  years  ago  scarcely  even  touched 
upon  these  quantitative  relations,  although  the  fundamental 
principles  of  electrical  measurement  had  been  fully  worked 
out  by  Gauss,  Weber,  Sir  William  Thomson,  and  a few 
others. 

It  was  the  application  of  electricity  to  practical  purposes 
which  changed  all  this;  and  especially  the  rapid  and  com- 
paratively recent  development  of  electric  lighting,  and  of  the 
application  of  electricity  to  the  distribution  of  power. 

An  electrical  engineer  requires  to  know  not  only  whether 
a current  will  be  produced  under  certain  circumstances,  but 
also  the  exact  effect  of  each  one  of  these  circumstances,  so 
that  he  may  be  able  to  determine  the  conditions  most  favor- 


70 


ELECTRICITY  IN  MODERN  LIFE 


able  to  its  economical  production,  and  design, his  apparatus 
and  system  of  distribution  accordingly. 

It  is  not  sufficient  for  him  to  know  that  a smaller  porpor- 
tion  of  euergy  is  wasted  in  the  form  of  heat  when  the  cur- 
rent is  carried  by  a copper  conductor  than  if  an  iron 
conductor  of  the  same  dimensions  were  employed.  He 
wants  to  know  exactly  how  much  one  is  better  than  the 
other,  so  that  he  may  be  able  to  decide  whether  it  is  more 
advantageous  to  incur  the  increased  expense  of  copper  con- 
ductors in  order  to  save  the  waste  of  energy,  or  whether 
the  increase  in  cost  would  more  than  counterbalance  the 
saving  effected  in  the  motive-power. 

If  the  balance  of  advantage  is  in  favor  of  copper — as  it 
invariably  is,  for  example,  in  the  case  of  the  conductors 
which  carry  the  currents  for  electric  lighting — he  has  to 
determine  the  most  economical  dimensions  of  the  conductors 
to  be  employed  in  carrying  the  current  required. 

This  is  a problem  which  has  to  be  determined  almost 
daily  in  the  case  of  laying  down  electric  light  cables,  which 
are  now  spreading  so  rapidly  even  in  London.  These  re- 
quirements of  the  practical  engineer,  which  began  to  make 
themselves  sensibly  felt  when  submarine  telegraphy  first 
became  a realized  fact,  afforded  a most  powerful  stimulus 
to  the  development  both  of  a system  of  electrical  measure- 
ment and  of  the  means  for  practically  carrying  it  out. 

If  the  development  of  the  system  itself  had  been  entirely 
in  the  hands  of  the  mathematical  electricians,  and  had  been 
uninfluenced  by  practical  considerations,  it  would  have  de- 
veloped much  more  slowly;  and  would  probably,  to  some 
extent  at  any  rate,  have  failed  to  fulfil  the  requirements 
of  the  practical  engineer. 

If,  on  the  other  hand,  it  had  been  developed  by  men 


ELECTRICAL  MEASUREMENT 


71 


acquainted  only  with  the  practical  side  of  the  question,' 
unaided  by  scientific  theory,  it  would  never  have  been  so 
simple  and  convenient,  even  for  practical  purposes,  as  that 
now  in  use.  It  would,  in  fact,  have  borne  the  same  relation 
to  the  actually  existing  system  that  our  English  system  of 
Weights  and  Measures  does  to  that  which  was  developed 
by  scientific  men  in  France,  which,  in  addition  to  being 
one  of  the  greatest  boons  to  the  population  of  the  country 
in  which  it  took  its  rise,  has  been  found  so  greatly  superior 
to  any  system  developed  without  the  aid  of  scientific  knowl- 
edge that  it  has  been  universally  adopted  for  the  purpose  of 
scientific  measurements,  and  has  been  made  the  basis  of  the 
practical  system  of  electrical  measurement. 

The  British  Association  Committee,  with  Sir  William 
Thomson  as  its  guiding  spirit,  played  the  most  important 
part  in  the  development  of  this  system,  which  is  now  in  use 
by  electrical  engineers  of  every  nationality,  and  in  every 
part  of  the  world  where  electricity  is  employed  for  practical 
purposes. 

The  foundation  of  the  science  of  electrical  measurement 
was  really  laid  by  the  investigations  of  Cavendish  about  the 
middle  of  the  last  century,  in  which  he  showed  that  the  ob- 
served fact  that  a hollow  electrical  globe  does  not  com- 
municate any  portion  of  its  charge  to  a small  globe  in 
communication  with  and  inclosed  within  it,  leads  by  strict 
mathematical  reasoning  to  the  conclusion  that  the  attraction 
between  two  small  electrically-charged  bodies  is  inversely 
proportional  to  the  square  of  the  distance  between  them. 
Until  Professor  Clark-Max  well  in  1879  edited  Cavendish’s 
unpublished  papers  the  French  physicist  Coulomb  had  gen- 
erally been  credited  with  this  discovery,  as  Cavendish, 

though  he  communicated  some  of  his  preliminary  results 

Science — Vol.  XTIT — 4 


72 


ELECTRICITY  IN  MODERN  LIFE 


to  the  Eoyal  Society  in  1771,  never  published  his  definite 
proof  of  the  law. 

Cavendish’s  prior  discovery  does  not  in  any  way  detract 
from  the  merit  of  Coulomb,  who  in  the  year  1875  commu- 
nicated to  the  French  Academy  the  description  of  a series 
of  experiments  with  his  torsion  balance,  in  which  he  had 
directly  demonstrated  the  law  of  inverse  squares  both  for 
electrical  action  and  for  the  attraction  and  repulsion  be- 
tween magnetic  poles.  The  discoveries  of  Cavendish  and 
Coulomb  laid  the  foundation  of  the  theory  of  electrostatics 
and  of  magnetism  respectively;  and  Oersted’s  discovery  in 
1820  of  the  mutual  actions  between  electric  currents  and 
magnets  formed  the  basis  on  which  Ampere  built  up  his 
mathematical  theory  of  electro-magnetism. 

It  has  been  pointed  out  in  Chapter  III.  that  these  inves- 
tigations gave  the  means  of  measuring  electric  currents  by 
their  actions  on  magnets  and  upon  each  other;  and,  indeed. 
Ampere  was  the  originator  both  of  the  idea  and  of  the  name 
of  the  Galvanometer. 

In  the  same  year  in  which  Ampere  described  this  instru- 
ment Schweigger  modified  Ampere’s  original  idea  by  wind- 
ing a wire  into  a coil,  in  the  centre  of  which  a magnetic 
needle  was  suspended,  and  indicated  by  its  deflections  the 
direction  and  strength  of  the  current  traversing  the  coil. 

In  the  year  1837  Pouillet  modified  this  instrument  so 
as  to  make  it  capable  of  exactly  comparing  the  strengths 
of  two  currents  by  means  of  the  respective  deflections'  of  the 
needles,  instead  of  the  deflection  only  giving  a general  idea 
of  the  current  strength.  The  “Sine”  and  “Tangent”  gal- 
vanometers, invented  by  him,  are  still  among  the  instru- 
ments in  most  frequent  use  for  laboratory  measurements 
of  electric  currents. 


ELECTRICAL  MEASUREMENT 


T6 


In  the  year  1846  Ampere’s  investigations  on  the  mutual 
actions  of  conductors  carrying  electric  currents  led  Weber 
to  the  invention  of  the  electro-dynamometer,  an  instrument 
in  which  an  electric  current  traverses  in  succession  a fixed 
coil  and  a small  movable  one  suspended  within  it,  and  the 
strength  of  the  current  is  determined  by  means  of  the  deflec- 
tion of  the  smaller  coil. 

While  advances  were  thus  being  made  in  the  construc- 
tion of  instruments  for  use  in  electrical  measurement,  the 
theory  of  the  subject  was  by  no  means  standing  still. 

In  the  year  1827  Ohm  published  a most  important  paper, 
in  which  he  showed  that  the  strength  of  the  current  between 
any  two  points  of  a conductor  is  proportional  to  the  electro- 
motive force  between  the  two  points,  divided  by  a certain 
quantity  depending  only  upon  the  dimensions  and  material 
of  the  conductor,  which  he  called  its  “electrical  resistance.” 

For  some  years  after  this  electricians  continued  to  follow 
Ohm’s  example  in  expressing  the  resistances  of  different 
portions  of  a circuit  in  terms  of  the  resistance  of  a selected 
portion  of  it. 

In  the  year  1837,  however,  Pouillet  took  the  very  impor- 
tant step  of  expressing  all  his  measurements  of  resistance  in 
terms  of  the  resistance  of  distilled  mercury,  using  as  a stand- 
ard the  resistance  of  a column  of  mercury  of  a measured 
length,  contained  in  a glass  tube,  terminating  in  wide  cups 
in  order  to  allow  of  the  necessary  connections  being  made. 

In  the  year  1833  Gauss  published  a most  important 
paper,  in  which  he  described  the  theory  and  method  of 
measuring  the  intensity  of  terrestrial  magnetism  and  the 
strength  of  a magnetic  pole  in  absolute  measure — that  is 
to  say,  in  terms  of  units  depending  only  on  the  units  of 
space,  time,  and  mass  which  were  chosen.  Those  adopted 

J 


74 


ELECTRICITY  IN  MODERN  LIFE 


by  him  were  the  millimetre,  the  second,  and  the  milli- 
gramme. 

In  1851  and  subsequent  years  Weber,  who  had  been 
associated  with  Grauss  in  his  magnetic  measurements,  devel- 
oped a definite  system  of  electrical  measurement  expressed 
in  terms  of  absolute  units,  and  founded  upon  Gauss’s  abso- 
lute system  of  magnetic  measurement.  In  a paper  pub- 
lished by  him  in  1851  he  pointed  out  that,  according  to 
Ohm’s  law,  the  resistance  of  a closed  circuit  is  determined 
in  terms  of  the  E.M.F.  and  the  current  strength,  and  he 
proceeded  to  define  the  unit  of  resistance  as  the  resistance 
of  a closed  circuit,  in  which  unit  E.M.F.  produces  a current 
of  unit  strength. 

He  then  went  on  to  show  that  E.M.F.  and  current 
strength  require  for  their  expression  in  absolute  measure 
only  the  determination  of  the  strength  of  a magnetic  pole, 
and  of  the  intensity  of  terrestrial  magnetism,  both  of  which 
Gauss  had  shown  how  to  determine. 

The  advantages  of  Weber’s  system  were  at  once  recog- 
nized by  Sir  W.  Thomson,  and  in  the  year  1861  a Com- 
mittee of  the  British  Association  was  appointed,  at  his 
suggestion,  for  the  consideration  of  standards  of  electrical 
resistance,  and  the  plan  of  work  was  subsequently  extended 
so  as  to  include  the  general  question  of  electrical  measure- 
ment. The  committee  thus  formed  requested  the  co-opera- 
tion of  the  principal  British  and  foreign  electricians,  includ- 
ing both  purely  scientific  men  and  practical  engineers;  and 
the  final  conclusion  at  which  they  arrived  was  to  adopt  a 
series  of  practical  units  obtained  by  taking  convenient  mul- 
tiples of  the  absolute  units.  The  principal  units  required 
by  practical  engineers  are  those  of  quantity,  of  current,  of 
resistance,  and  of  potential  or  E.M.F. 


ELECTRICAL  MEASUREMENT 


75 


Now,  Ohm’s  law  gives  a relation  between  the  last  three 
of  these,  and  the  first  two  are  very  simply  related;  so  it 
is  sufiicient  to  determine  any  two  of  them.  It  will  greatly 
assist  the  reader  in  forming  a conception  of  the  quantitative 
relations  which  have  to  be  considered  by  electrical  engineers 
to  understand  clearly  how  these  units  are  obtained,  and  1 
shall  therefore  indicate  very  briefly  the  simple  course  of 
reasoning  by  which  the  units  of  current  and  resistance  are 
expressed  in  terms  of  absolute  units. 

Coulomb’s  experiments  had  shown  that  the  force  acting 
between  two  magnetic  poles  is  proportional  to  the  product 
of  their  strengths  divided  by  the  square  of  the  distance  be- 
tween them;  and  therefore,  unless  a useless  factor  is  intro- 
educed,  the  force  may  be  defined  as  equal  to  this  expression; 
from  which  it  will  follow  that  the  unit  pole,  or  pole  of  unit 
strength,  will  be  that  which  repels  a similar  pole  at  a dis- 
tance of  one  centimetre,,  with  a force  of  one  dyne. 

Now,  the  force  exerted  on  a unit  magnetic  pole  by  a 
current  whose  distance  from  it  is  constant — that  is  to  say, 
by  a current  flowing  in  a conductor  in  the  form  of  a circular 
arc  described  with  the  pole  as  centre — is  found  to  be  pro- 
portional to  the  length  of  the  arc  divided  by  the  square  of 
the  radius  of  the  circle,  and  therefore  the  force  on  a mag- 
netic pole  may  be  defined  as  being  equal  to  the  product 
of  the  length  of  the  arc,  the  current  through  it,  and  the 
strength  of  the  pole,  divided  by  the  square  of  the  radius; 
and  it  follows  that  the  unit  current  must  be  defined  as  the 
current  of  which  each  centimetre  exerts  a force  of  one  dyne 
on  a unit  magnetic  pole  at  a distance  of  a centimetre. 

The  unit  of  electric  quantity  is  defined  as  the  quantity 
conveyed  in  one  second  by  a current  of  unit  strength. 

It  is  found  that  the  work  required  to  transfer  a given 


76 


ELECTRICITY  IN  MODERN  LIFE 


quantity  of  electricity  from  one  point  to  another  of  a con- 
ductor is  equal  to  the  product  of  the  quantity  transferred 
into  the  electro-motive  force  between  the  two  points,  and 
therefore  the  unit  electro-motive  force  is  an  electro-motive 
force,  such  that,  if  it  is  established  between  two  points,  an 
amount  of  work  equal  to  one  Erg  will  be  required  to  trans- 
fer the  unit  quantity  of  electricity  from  one  to  the  other. 
The  unit  of  resistance  is  then  defined  in  accordance  with 
Ohm’s  law,  which  asserts  that  the  resistance  between  two 
points  of  a conductor  is  measured  by  the  ratio  of  the  electro- 
motive force  between  them  to  the  current  produced  by  it. 

The  unit  of  resistance  is  therefore  defined  as  the  resist- 
ance of  a conductor  in  which  unit  electro-motive  force 
produces  unit  current. 

The  units  so  obtained  are  not  altogether  of  convenient 
magnitude  for  the  expression  of  the  electrical  quantities 
which  most  commonly  occur  in  practical  work,  some  being 
too  large  and  others  too  small. 

The  practical  importance  of  selecting  units  of  suitable 
magnitude  may  easily  be  seen  by  considering  what  would 
be  the  result  if,  on  the  one  hand,  drapers  were  to  use  a mile 
as  the  unit  of  length  in  selling  silk  to  their  retail  customers; 
or  if,  on  the  other  hand,  the  dates  of  events,  referred,  as  is 
usual,  to  the  beginning  of  the  Christian  era,  were  stated  in 
seconds  instead  of  years.  The  result  would  be  that  in  the 
first  case  the  quantities  of  silk  most  commonly  sold  would 
have  to  be  expressed  by  means  of  decimal  fractions  of  the 
unit;  while  in  the  second  illustration  the  number  of  figures 
employed  would  be  utterly  unwieldy. 

The  units  defined  above,  being  based  on  the  centimetre 
as  a measure  ot  length,  the  gramme  as  a measure  of  mass, 
and  the  second  as  a measure  of  time,  are  known  as  centi- 


ELECTRICAL  MEASUREMENT 


77 


metre,  gramme,  second  (usually  denoted  by  their  initial 
letters  C.G.S.)  units. 

The  practical  unit  of  electric  current  is  defined  as  one- 
tenth  of  the  C.Gf.S.  unit  of  current,  and  is  called  an  Ampere, 
after  the  great  French  electrician  of  that  name.  The  unit 
of  electro-motive  force  is  called  a Yolt,  after  Volta,  and  is 
taken  to  be  a hundred  million  O.Gr.S.  units.  The  unit  of 
resistance,  which  is  called  the  Ohm,  is  then  defined  as  the 
resistance  of  a conductor  through  which  an  electro-motive 
force  of  one  Volt  will  produce  a current  of  one  Ampere. 

It  can  be  shown  to  follow  from  these  definitions  that  the 
Ohm  is  equal  to  a thousand  million  C.Gr.S.  units. 

The  unit  of  quantity  is  called  the  Coulomb,  and  is  de- 
fined to  be  the  quantity  of  electricity  carried  by  the  unit 
current  in- a second.  Its  value  is  one-tenth  of  a O.Gr.S.  unit. 

These  units  came  into  general  use,  in  Great  Britain  and 
her  Colonies,  during  the  years  1870  and  1871,  through  the 
influence  of  the  British  Association  Committee. 

On  the  continent  of  Europe,  however,  the  absolute  sys- 
tem was  not  generally  adopted  for  practical  purposes  until 
after  the  meeting  of  the  International  Congress  of  Elec- 
tricians which  was  held  in  Paris  in  October,  1881,  when 
it  was  decided  that  they  should  be  adopted  by  electricians 
throughout  the  world. 

The  process  of  determining  either  the  Volt  or  the  Ohm 
in  absolute  measure  is  one  of  great  difficulty,  and  requiring 
the  most  elaborate  precautions.  The  result  of  this  was  that 
at  the  time  of  the  Paris  Congress  numerous  discrepancies 
existed  between  the  experimental  determinations  of  various 
eminent  electricians;  and  it  was  therefore  decided  to  define 
provisionally  a “Legal  Ohm”  as  the  resistance  of  a column 
of  pure  mercury  106  centimetres  long,  and  having  a sec- 


78 


ELECTRICITY  IN  MODERN  LIFE 


tional  area  of  one  square  centimetre,  this  length  being  the 
nearest  whole  number  to  the  mean  of  the  most  reliable  of 
the  results  obtained.  The  Volt  was  therefore  defined  as  the 
B.M.F.  which  maintains  a current  of  an  Ampere  in  a, con- 
ductor whose  resistance  is  a Legal  Ohm.  The  Coulomb 
and  Ampere  retained  their  former  definitions. 

The  unit  of  power  employed  by  electrical  engineers  is 
defined  electrically  as  the  power  developed  in  a circuit 
traversed  by  a current  of  one  Ampere  with  a potential  dif- 
ference at  its  terminals  of  one  Volt.  This  unit,  which  is 
called  a Watt,  is  equivalent  to  ten  million  Ergs  per  second. 


ELECTRIC  MACHINES 


79 


CHAPTEE  VIII 

MAGNETO  AND  DYNAMO  ELECTRIC  MACHINES 

WHEN  Faraday  had  discovered  that  electric  currents 
could  be  produced  by  the  motion  of  a conductor 
in  a magnetic  field,  he  constructed  a machine  by 
which  a continuous  current  could  be  conveniently  generated 
in  this  manner.  It  consisted  of  a disk  of  copper  twelve 
inches  in  diameter,  and  about  one-fifth  of  an  inch  thick, 
fixed  upon  a brass  axle,  about  which  it  was  made  to  rotate 
with  its  edge  between  the  poles  of  a large  compound  per- 
manent steel  magnet,  formed  by  joining  a number  of  steel 
horseshoe  magnets  together,  the  poles  being  about  half  an 
inch  apart. 

The  current  was  made  to  pass  through  a pair  of  conduct- 
ing wires  or  leads,  one  of  which  was  attached  to  a brass 
axle,  and  the  other  to  a copper  strip,  which  rubbed  against 
the  edge  of  the  disk  between  the  poles  of  the  magnet. 

Faraday  then  found  that,  if  a galvanometer  was  included 
in  the  circuit  with  the  conducting  wires,  a permanent  deflec- 
tion was  produced,  of  an  amount  varying  with  the  speed 
of  rotation;  and  that  it  was  reversed  when  the  direction  of 
rotation  was  reversed.  This  was  the  first  magneto-electric 
machine.  It  was  followed  by  a number  of  devices,  in  which 
coils  of  wire  were  made  to  rotate  between  the  poles  of  a 


80 


ELECTRICITY  IN  MODERN  LIFE 


permanent  steel  magnet;  or  in  which  the  magnet  was  made 

to  rotate,  while  the  coils  of  wire  remained  fixed  between  the 

* 

revolving  poles. 

Now,  the  use  of  steel  magnets  greatly ' restricted  the 
power  of  these  machines,  for  very  large  steel  magnets  are, 
in  the  first  place,  costly  to  build  up,  and,  in  the  second 
place,  they  gradually  lose  a considerable  portion  of  their 
magnetism. 

In  the  year  1845  Wheatstone  and  Cooke  took  out  a patent 
for  the  use  of  electro-magnets  instead  of  permanent  steel 
magnets;  and  three  years  later  Jacob  Brett  suggested  that 
the  current  generated  in  the  armature  by  the  permanent 
magnetism  of  the  field  "magnets  should  be  sent  through 
a coil  of  wire  surrounding  the  latter,  so  as  to  increase  their 
strength. 

This  appears  to  be  the  first  suggestion  of  the  principle 
of  the  self-exciting  dynamo. 

In  1863  Wilde  devised  a machine  in  which  an  armature, 
consisting  of  coils  of  wire,  was  made  to  rotate  between  the 
poles  of  a large  electro-magnet,  which  was  excited  by  means 
of  a separate  small  magneto-machine. 

The  term  “dynamo-electric  machine”  was  first  introduced 
by  Dr.  Werner  Siemens  in  1867  in  describing  to  the  Berlin 
Academy  machines  in  which  currents  were  induced  ix  the 
coils  of  the  rotating  armature  by  means  of  electro-magnets, 
which  were  themselves  excited  by  the  currents  in  the  arma- 
ture. This  term,  in  its  shortened  form  of  “dynamo,”  is 
now  employed  for  all  electrical  machines  driven  by  mechan- 
ical power,  whether  self-exciting  or  not,  in  which  the 
current  is  generated  by  the  motion  of  coils  of  wire  in  a 
magnetic  field,  or  by  the  rotation  of  a magnetic  field  about 
coils  of  wire.  Since  this  time  the  theory  and  practice  of 


ELECTRIC  MACHINES 


81 


dynamo  construction  have  advanced  with  rapid  strides,  and 
the  various  dynamos  now  in  use  are  so  numerous  that  they 
would  require  a volume  very  much  larger  than  the  present 
one  for  their  description. 

An  ideally  simple  dynamo  is  shown  in  the  illustration 
(Fig.  6). 

It  consists  of  a simple  rectangular  loop  of  wire  rotating 
between  the  poles  of  a large  magnet,  and  therefore,  as  has 
been  pointed  out  before,  in  an  approximately  uniform 
magnetic  field. 

When  the  loop  is  vertical,  as  shown  in  the  figure,  it  will 
be  traversed  from  left  to  right  by  the  maximum  number 
of  unit  tubes  of  force ; this 
number  will  diminish  to 
zero  when  the  plane  of 
the  loop  is  horizontal,  and 
after  another  quarter  revo- 
lution— that  is  to  say,  after 
half  a revolution  from  its 
original  position — the  loop  will  again  be  traversed  by  the 
maximum  number  of  unit  tubes  of  force.  They  will  now 
pass  through  it  in  a direction  opposite  to  their  former  direc- 
tion, owing  to  the  aspect  of  the  loop  with  respect  to  the 
magnetic  field  having  been  reversed.  Starting  from  the  posi- 
tion shown  in  the  figure,  the  currents  generated  in  the  loop 
during  the  first  half  revolution  will  be  all  in  the  same  direc- 
tion. During  the  first  quarter  revolution  the  number  of  unit 
tubes  of  force  passing  through  the  loop  will  be  diminishing, 
while,  during  the  next  quarter  revolution,  they  will  be 
increasing,  and  passing  through  the  loop  in  the  opposite 
direction,  so  that  the  effect  will  be  the  same.  There  will 
therefore  be  a current  in  one  direction  round  the  loop  during 


82 


ELECTRICITY  IN  MODERN  LIFE 


the  first  half  revolution,  and  the  opposite  way  round  daring 
the  second  half  revolution.  In  order  to  send  these  currents 
through  the  conducting  wires  in  the  same  direction,  a com- 
mutator of  the  kind  shown  in  Fig.  6 may  be  used.  It 
consists  of  two  nearly  semicircular  segments  of  metal  tube 
mounted  on  a cylinder  of  hard  wood  or  other  convenient 
insulating  substance.  Each  of  these  segments  is  connected 
with  one  end  of  the  loop,  and  a couple  of  strips  of  metal 
are  connected  with  the  leads,  and  collect  the  current  from 
the  armature  by  pressing  against  the  split  tube,  as  shown  in 
the  diagram. 

If  the  lines  of  force  in  the  field  were  perfectly  horizontal, 
these  strips,  or  brushes,  as  they  are  called,  would  have  to 
be  set  so  as  to  reverse  the  connections  as  the 
plane  of  the  loop  passed  through  the  vertical 
position;  but  it  is  found  in  practice  that  the 
brushes  must  be  displaced  slightly  in  the  direc- 
tion of  rotation  of  the  armature. 

This  displacement  is  called  the  lead  of  the 
brushes,  and  there  has  been  considerable  difference  of 
opinion  as  to  why  it  is  necessary. 

It  is  now  known,  however,  that  it  is  really  due  to  the 
lines  of  force  being  turned  into  a slightly  oblique  position 
by  means  of  the  currents  in  the  armature. 

It  is  found  that  if  a mass  of  iron  is  placed  within  the 
armature  it  will  cause  a large  number  of  unit  tubes  of  force 
to  thread  through  the  loop,  the  tubes  which  would  otherwise 
pass  outside  the  armature  being  attracted,  as  it  were,  by  the 
iron,  and  made  to  pass  through  its  mass. 

When  the  field  magnets  are  stationary  and  the  armature 
is  made  to  revolve,  this  mass  of  iron,  or  core,  as  it  is  called, 
should  really  be  at  rest,  because  if  it  rotates  with  the  arma- 


ELECTRIC  MACHINES 


83 


ture,  currents  will  be  induced  within  it,  just  as  in  the  copper 
disk  of  Faraday’s  machine,  and  these,  while  absorbing  some 
of  the  energy  from  the  driving  machinery,  will  not  con- 
tribute anything  to  the  current  in  the  circuit. 

It  is,  however,  easy  to  see  that  there  would  be  consider- 
able structural  difficulties  to  be  overcome  in  fixing  a station- 
ary mass  of  iron  within  the  revolving  armature,  and  so  it  is 
usually  made  to  revolve  with  the  armature.  In  order  to 
reduce  as  far  as  possible  the  currents  induced  in  the  core, 
and  which  are  known  as  eddy  currents,  the  cores  are  built 
up  of  thin  sheets  of  iron,  separated  from  one  another  by 
means  of  varnish,  mica,  asbestos  paper,  or  other  convenient 
insulating  substance. 

In  addition  to  the  waste  of  energy  caused  by  these  eddy 
currents,  they  heat  the  core  considerably,  and  therefore, 
even  independently  of  the  waste  of  energy,  solid  iron  cores 
are  inadmissible,  for  the  heating  of  the  core  which  would 
ensue  would  not  only  increase  the  resistance 
of  the  armature  coils,  and  therefore  diminish 
the  currents  induced  in  them,  but  would  de- 
stroy the  insulating  material  which  separates 
the  different  turns  of  the  coils.  In  practice  the 
armature  is  never  formed  of  a single  loop,  but 
of  a coil,  such,  for  example,  as  is  shown  in  Fig.  7,  which 
exhibits  a section  of  the  original  form  of  Siemens’s  shuttle- 
wound  armature,  consisting  of  a coil  of  wire  wound  upon 
an  iron  core.  Siemens’s  original  magneto-machine,  with  an 
armature  of  this  kind,  and  permanent  steel  magnets,  is 
shown  in  Fig.  8.  This  form  of  armature  is  still  retained 
in  small  motors,  but  for  larger  machines  it  has  been  entirely 
replaced  by  armatures  in  which  the  coils  are  wound  upon 
a ring  or  drum  of  iron,  and  which  are  therefore  known  as 


84 


ELECTRICITY  IN  MODERN  LIFE 


ring  armatures  and  drum  armatures  respectively.  Fig.  9 
shows  a simple  ring  armature  with  a single  coil. 

Now  if  a shuttle-wound,  or  a single  ring-armature  with 


Fig.  8. 

one  coil,  is  employed,  with  a split  tube  commutator,  al- 
though the  currents  in  the  leads  will  always  be  in  the  same 

direction,  they  will  not  be  of  constant 
strength,  but  will  vary  from  a maxi- 
mum to  zero  at  each  half  revolution. 
To  remedy  this,  the  ring  or  drum- 
armature  is  made  with  a number  of 
coils,  and  the  tube  of  the  commutator, 
instead  of  being  divided  into  two  seg- 
ments only,  is  divided  into  as  many 
segments  as  there  are  coils. 

The  coils  of  the  armature  then  come  into  action  in  succes- 
sion when  they  are  in  the  position  for  best  action.  A ring- 
armature  of  this  kind  is  shown  in  Fig.  10. 


ELECTRIC  MACHINES 


85 


Here  the  armature  coils  are  all  in  continuous  connection; 
but  in  some  machines,  such,  for  example,  as  the  well-known 
Brush  machine,  the  coils  are  all  separate,  and  each  coil  has 
its  own  commutator.  A four-part  drum-armature,  with  its 
commutator  and  collecting  brushes,  is  shown  in  Fig.  11. 


Fig.  10. 


'There  are  also  disk-armatures,  in  which  the  coils  are  flat- 
tened against  the  disk,  and  pole-armatures,  which  have  the 
coils  wound  upon  separate  poles  projecting  radially  from 
the  periphery  of  the  disk,  as  shown  in  Fig.  12,  which  exhibits 
a six-pole  armature  with  commu- 
tator and  collecting  brushes. 

Methods  of  Exciting  the  Field 
Magnets, — There  are  five  simple  - 
ways  of  producing  the  Magnetic 
Field  in  which  the  armature  of 
the  dynamo  rotates.  Of  these 
methods  the  one  first  employed 
consists,  as  has  already  been 
pointed  out,  in  the  use  of  a per- 
manent steel  magnet.  Fig.  13 
shows,  in  a diagrammatic  form,  a machine  of  this  kind  with 
its  circuit. 

The  terminals  of  the  armature  coils,  together  with  the 
collecting  brushes,  are  seen  between  the  poles  of  the  mag- 


86 


ELECTRICITY  IN  MODERN  LIFE 


net;  and  the  arrows  show  the  direction  of  the  current  in  the 
circuit  when  the  armature  revolves  as  indicated  by  the  posi- 


Fig.  12. 


tion  of  the  brushes — viz.,  in  the  direction  of  the  hands 
of  a watch.  It  will  be  seen  that  this  is  simply  the  old 

magneto-electric  machine  which 
formed  the  original  of  the  mod-' 
ern  dynamo;  but  as  the  latter  is 
now  adopted  as  a generic  term 
for  all  these  machines,  I shall 
follow  Professor  S.  P.  Thompson 
in  calling  it  a magneto-dynamo. 

Permanent  steel  magnets  are 
now  only  employed  for  quite 
small  machines,  numerous  types 
of  which,  for  laboratories  and 
other  purposes,  are  still  made 
with  them. 

In  order  to  regulate  the 
E.M.F.  produced  by  a machine 
of  this  kind  a movable  piece  of 
iron  is  usually  provided,  which 
can  be  placed  more  or  less  over 
the  poles  of  the  Field  Magnet,  in  such  a way  as  to  divert 
a certain  portion  of  the  magnetism  from  the  armature. 


Fig.  13. 


ELECTRIC  MACHINES 


87 


The  second  stage  in  the  development  of  the  dynamo  is 
shown  in  Fig.  14,  which  represents  a separately  excited 
dynamo — that  is  to  say,  one  in  which  the  magnetic  field  is 
produced  by  means  of  an  -electro-magnet,  the  magnetism 
of  which  is  excited  from  some  external  source,  such  as  a vol- 
taic battery,  or  by  means  of  a small  auxiliary  magneto- 
dynamo, as  was  done  by  Wilde  in  1866. 

The  arrows  in  the  diagram  show  the  direction  of  the 
current  in  the  field  magnet 
coils  required  to  produce 
the  polarity  indicated,  and 
the  direction  of  the  cur- 
rent in  the  main  circuit 
when  the  rotation  is  in  the 
same  direction  as  before. 

The  separately  excited  dy- 
namo may  be  governed  in 
the  same  way  as  the  mag- 
neto-dynamo; but  there 
are  two  other  methods  of 
regulating  its  E.M.F.,  one 
or  other  of  which  will 
generally  be  found  prefer- 
able. These  consist  either 
in  weakening  the  current, 
which  may  be  convenient- 
ly effected  by  introducing 
additional  resistance  into  its  circuit,  or  in  altering  the 
number  of  convolutions  of  wire  through  which  the  exciting 
current  circulates  round  the  field  magnets. 

In  any  dynamo  the  magnetic  field  is  necessarily  modified 
by  the  current  in  the  armature  coils,  the  effect  of  the  field 


88 


ELECTRICITY  IN  MODERN  LIFE 


due  to  the  armature  being  to  produce  an  B.M.F.  in  the 
opposite  direction  to  that  due  to  the  primary  field,  and 
therefore  known  as  the  back  E.M.F. 

It  is  evident  that  the  strength  of  the  back  E.M.F.  will 
increase  with  the  speed  of  rotation,  provided  the  resistance 
in  the  main  circuit  remains  unchanged;  but  it  will  be 
diminished  by  increasing  this  resistance — that  is,  by  giving 
the  machine  more  work  to  do;  for  example,  by  putting  a 
larger  number  of  lamps  into  the  circuit. 

With  the  exception  of  the  effect  of  this  back  E.M.F.,  it 
is  clear  that  in  both  these  machines  the  E.M.F.  will  be  inde- 
pendent of  the  resistance  in  the  main  circuit. 

The  next  stage  in  the  development  of  the  dynamo  was 
to  do  away  with  the  auxiliary  exciter,  and  make  the  machine 
excite  its  own  magnetism. 

This  is  effected  by  making  use  of  the  current,  or  of  a 
portion  of  the  current,  developed  in  the  armature,  to  excite 
the  field  magnets.  It  would  evidently  be  impossible  to  start 
this  process  unless  the  field  magnets  were  excited  to  a cer- 
tain extent  to  begin  with. 

Assuming  this  to  be  the  case,  it  is  easy  to  see  that  the 
small  current  which  will  be  produced  by  rotating  the  arma- 
ture may  be  made  to  increase  their  magnetism,  and  that  the 
resulting  increased  strength  of  the  magnetic  field  will  in- 
crease the  current  through  the  armature,  which,  in  its  turn, 
will  still  further  magnetize  the  field  magnets;  so  that  in  this 
way,  starting  with  a very  small  initial  magnetization  of  the 
field  magnets,  it  may  be  increased  up  to  any  desired  extent 
below  that  of  saturation.  It  is  found  in  practice  that  this 
process  can  be  started  without  initially  magnetizing  the 
field  magnets  from  a separate  source,  the  reason  being  that 
iron  is  always  slightly  magnetic;  and  although  its  residual 


ELECTRIC  MACHINES 


89 


magnetism,  as  it  is  called,  may  be  so  small  as  to  require 
exceedingly  delicate  instruments  to  detect  it,  it  is  invariably 
found  to  be  sufficient,  without  external  assistance,  to  start 
the  process  of  self-excitation. 

There  are  three  simple  types  of  self-exciting  dynamo. 
The  first  and  simplest  of  these,  which  may  be  called  the 
ordinary  dynamo,  is  known  to  electricians  as  the  series 
dynamo.  It  is  illustrated  dia- 
grammatically  in  Fig.  15,  and 
it  will  be  seen  from  the  illus- 
tration that  the  whole  of  the 
current  from  the  armature 
passes  through  the  exciting 
coils,  which  are  connected  in 
series  with  the  main  circuit. 

This  form  of  machine  has 
several  serious  disadvantages. 

In  the  first  case,  it  is  liable 
to  become  reversed  in  polari- 
ty, which  makes  it  impossible 
to  use  it,  either  for  electro- 
plating purposes,  or  for  charg- 
ing accumulators  or  secondary 
batteries. 

In  the  second  place,  it 
will  not  begin  to  excite  itself 
until  a certain  speed  has  been  attained,  depending  on  the 
resistance  in  the  circuit. 

Finally,  it  has  the  disadvantage  that  any  increase  in  the 
resistance  of  the  main  circuit  diminishes  the  exciting  cur- 
rent, and  therefore  diminishes  the  E.M.F.  produced  by  the 
machine. 


Fig.  15. 


90 


ELECTRICITY  IN  MODERN  LIFE 


The  serious  nature  of  this  last  disadvantage  will  easily 
be  understood  by  considering  its  effect  when  the  machine 
is  used  to  supply  current  for  an  electric  light  circuit.  Arc 
lamps,  such  as  are  used  for  street  lighting  and  for  large 
interiors  such  as  railway  stations,  are  usually  connected  in 
series — that  is  to  say,  the  main  circuit  wire  is  cut  wherever 
a lamp  is  to  be  inserted,  and  the  two  free  ends  ,thus  ob- 
tained are  joined  to  the  lamp  terminals. 

If  additional  lamps  are  put  into  such  a circuit  they  will 
increase  its  resistance,  and  therefore  diminish  the  power  of 
the  machine  just  when  it  ought  to  be  increased.  Incan- 
descent lamps,  on  the  other  hand,  such  as  are  used  for 
house  lighting  and  in  theatres,  are  usually  connected  in 
parallel — that  is  to  say,  the  conducting  wire  joining  the 
poles  of  the  dynamo,  and  forming  the  main  circuit,  is  con- 
tinuous; and  the  direct  and  return  portions  of  the  conductor 
— or  the  positive  and  negative  mains,  as  they  are  called — 
are  connected  across  at  various  points  through  the  lamps. 
In  this  case  the  addition  of  extra  lamps  to  the  circuit  opens 
up  additional  paths  for  the  electricity  to  traverse,  and 
therefore  diminishes  the  resistance  in  the  circuit,  so  that 
a smaller  B.M.F.  is  required  to  maintain  the  same  current. 
The  diminution  in  the  resistance,  however,  increases  the 
current  through  the  field  magnets,  and  this  causes  an  in- 
crease in  the  E.M.F.  developed  by  the  machine. 

In  order  to  overcome  some  of  the  defects  of  the  series 
dynamo,  another  type  of  machine,  shown  in  Fig.  16,  has 
been  devised.  In  this  machine,  as  is  shown  in  the  diagram, 
the  field  magnet  coils  are  not  connected  in  series  with  the 
main  circuit;  but  their  terminals,  and  those  of  the  main 
circuit,  are  both  connected  directly  to  the  collecting  brushes. 
The  two  circuits  are  then  said  to  be  in  parallel,  and  the 


ELECTRIC  MACHINES 


91 


series  coils  are  said  to  form  a shunt  to  the  main  circuit; 
whence  this  form  of  machine  is  known  as  a “shunt”' 
dynamo.  The  field  magnet  coils  are  made  of  a great 
number  of  turns  of  very  fine  wire,  so  that  they  have  a 
much  higher  resistance  than  that  of  the  main  circuit, 
and  are  therefore  traversed  by  a small  portion  only  of  the 
total  current. 

When  a “shunt”  dynamo  is  used  to  supply  a current  for 
a set  of  lamps  in  series,  the 
addition  of  lamps  to  the  cir- 
cuit sends  an  additional  pro- 
portion of  the  current  through 
the  field  magnet  coils,  and 
thus  increases  the  strength  of 
the  magnetic  field,  and  there- 
fore also  the  E.M.F.  devel- 
oped. If  the  machine  is  used 
to  supply  lamps  in  parallel, 
the  resistance  of  the  circuit  is 
diminished,  and  less  current 
is  sent  through  the  shunt 
coils,  so  that  the  strength  of 
the  field,  and  therefore  the 
E.M.F.  developed  by  the  ma- 
chine, is  slightly  diminished; 
and  if  the  internal  resistance 
of  the  armature  is  small,  such 
a machine  can  be  made  to  regulate  itself  fairly  well. 

The  principal  objection  to  shunt  wound  machines  is  that 
any  unsteadiness  in  the  driving  machinery  produces  a com- 
paratively large  effect  on  the  main  circuit.  The  reason  of 
this  is  that  the  shunt  coils,  being  formed  of  a great  many 


Fig.  16. 


92 


ELECTRICITY  IN  MODERN  LIFE 


turns  of  thin  wire  very  close  together,  and  wound  upon  an 
iron  core,  have  much  more  self-induction  than  the  main 
circuit,  and  therefore  any  variation  in  the  speed  produces 
its  effect  upon  the  lamps  before  the  current  in  the  exciting 
circuit  has  had  time  to  undergo  a sensible  change.  Shunt 
dynamos  are  easily  governed  by  introducing  resistance  into 
the  exciting  circuit. 

The  last  of  the  simple  forms  of  self-exciting  dynamo  is 
what  Professor  Thompson  calls  the  separate  circuit  self- 
exciting dynamo.  In  machines  of  this  type  the  “exciting” 
circuit  is  entirely  separate  from  the  main  circuit,  and  the 
current  through  it  is  obtained  either  from  a second  armature 
spinning  between  the  same  field  magnets,  or  through  a 
special  commutator  connected  separately  with  a few  of  the 
armature  coils,  and  supplying  no  current  to  the  main  circuit. 

Neither  series  nor  shunt  winding  can  be  employed  for 
alternating  current  machines,  but  either  of  the  systems 
described  may  be  employed  in  continuous  current  dynamos 
— viz.,,  those  which  give  a current  always  in  the  same 
direction. 

In  alternate  current  dynamos  no  commutator  is  required 
for  transmitting  the  current  to  the  main  circuit,  as  the  cur- 
rents, rapidly  succeeding  each  other  in  opposite  directions, 
are  sent  through  the  circuit  just  as  they  are  received  from 
the  machine,  and  therefore,  with  a rotating  armature,  a 
simple  sliding  contact  is  all  that  is  required. 

In  some  machines — such,  for  example,  as  those  in  use  at 
the  West  Brompton  Central  Electric  Lighting  Station — the 
armature  remains  at  rest  and  the  field  magnets  are  made  to 
rotate;  and  in  this  case  no  sliding  contact  is  required,  the 
terminals  of  the  main  circuit  being  attached  permanently 
to  the  armature.  When  the  machine  is  a self -exciting  one, 


ELECTRIC  MACHINES 


93 


it  is  liowever  necessary  to  employ  a commutator  to  rectify 
the  alternations  in  the  exciting  current. 

The  armature  coils  used  for  exciting  the  field  magnets 
are  therefore  connected  to  a commutator,  of  which  Pig.  17 
represents  a typical  form.  It  consists 
of  two  hollow  metal  cylinders  provided 
with  teeth,  and  fixed  upon  a solid  in- 
sulating cylinder,  the  teeth  of  either 
cylinder  projecting  between  those  of 
the  other  without  touching  them,  as 
is  shown  in  the  illustration.  The  two 
collecting  brushes  are  fixed  so  that  one 
is  always  in  contact  with  a tooth  of 
one  of  these  cylinders,  while  the  second  is  in  contact  with 
a tooth  of  the  other  one.  The  two  hollow  cylinders  form 
the  terminals  of  the  exciting  coils  of  the  armature. 


Fig.  17. 


94 


ELECTRICITY  IN  MODERN  LIFE 


CHAPTER  IX 

THE  STORY  OF  THE  TELEGRAPH 

SOME  of  the  descriptions  which  have  come  down  to  us 
of  the  manner  in  which  the  decrees  of  the  old  Roman 
oracles  were  communicated  to  those  who  consulted 
them,  irresistibly  suggest  that  magnetism  was  one  of  the 
agents  employed  by  the  priests  to  deceive  their  dupes.  The 
descriptions  are  naturally  extremely  vague,  as  the  narrators 
themselves  had  no  idea  whatever  of  the  process  employed. 

It  is  stated  in  one  of  these  accounts  that  an  iron  tripod 
turned  round  in  obedience  to  the  incantations  of  the  presid- 
ing priest,  accompanied  by  certain  movements,  the  object 
of  which  the  narrator  did  not  understand,  of  an  iron  ring 
suspended  from  a cord  which  the  priest  held  in  his  hand. 
The  letters  of  the  alphabet,  inscribed  on  separate  small 
plates,  were  arranged  round  the  tripod,  and  as  the  latter 
moved  they  were  drawn  down  upon  the  table  in  such  an 
order  as  to  spell  out  the  answer  of  the  oracle. 

It  is  very  clear  that  these  effects  might  be  produced 
by  means  of  magnetism,  and  it  is  difficult  to  imagine  what 
other  means  could  have  been  employed.  It  is  moreover 
quite  certain  that  the  lodestone  was  known  to  the  priests 
of  ancient  Egypt,  and  possibly  through  them  to  those  of 
ancient  Rome;  and  that  the  priests  were  also  acquainted 


THE  STORY  OF  THE  TELEGRAPH 


95 


with  the  fact  that  a steel  needle  rubbed  with  a lodestone, 
and  suspended  so  that  it  could  turn  freely  in  any  direction, 
would  set  itself  pointing  north  and  south. 

All  through  the  Middle  Ages  the  magnet  was  employed 
as  a means  of  imposition,  both  by  those  who  professed  to 
foretell  the  future,  and  by  the  quacks  who  pretended  to  pos- 
sess the  power  of  curing  all  the  ills  that  flesh  is  heir  to. 

Even  the  enlightenment  of  the  nineteenth  century  has 
not  extinguished  the  latter  class  of  impostors,  and  it  is  not 
therefore  difficult  to  imagine  how  easily  they  could  impose 
upon  the  credulity  of  the  multitude  in  what  are  generally 
known  as  the  dark  ages.  We  learn  again  from  many 
writers,  beginning  from  an  early  date  down  to  as  late  as 
the  seventeenth  century,  that  there  was  a widely-spread 
belief  in  the  possibility  of  communication  between  distant 
friends  by  means  of  the  magnet. 

The  method  by  which  this  was  supposed  to  be  effected 
usually  consisted  in  balancing  a pair  of  steel  needles,  which 
had  been  rubbed  with  the  same  lodestone,  upon  vertical 
axes  resting  on  circular  bases,  round  the  circumferences 
of  which  were  inscribed  the  letters  of  the  alphabet. 

It  was  then  stated  that  if  two  friends  each  possessed  one 
of  these  instruments,  then,  no  matter  how  far  apart  they 
might  be,  they  could  carry  on  conversation  by  their  means, 
the  method  of  procedure  being  simply  for  the  one  who 
wished  to  speak  to  take  his  instrument  and  turn  the  needle 
in  succession  to  the  different  letters,  so  as  to  spell  out  the 
sentence  required,  upon  which,  it  was  stated,  the  needle 
of  the  distant  instrument  would  move  from  letter  to  letter 
in  sympathy  with  the  first.  Such  statements  are,  of  course, 
absurd,  and  they  probably  originated  in  deliberate  impos- 
ture with  the  object  of  obtaining  money  from  the  credulous. 

Science — Vol.  XIII — 6 


96 


ELECTRICITY  IN  MODERN  LIFE 


The  famous  philosopher  Galileo  tells  us  that  he  was 
sought  out  by  one  of  these  impudent  impostors,  who  offered 
to  sell  him  a secret  art  which  would  enable  him,  by  means 
of  the  attraction  of  a certain  magnetic  needle,  to  converse 
across  distances  of  several  thousand  miles.  Galileo,  how- 
ever, was  not  the  kind  of  man  to  be  made  a dupe,  and  he 
very  pertinently  suggested  to  the  would-be  vender  that 
he  should  first  put  his  art  to  the  test  by  speaking  from 
one  corner  of  the  room  to  the  other.  This,  however,  did 
not  suit  the  impostor,  who  objected  that  the  distance  would 
be  too  short,  and  that  the  instruments  would  only  work 
when  the  space  separating  them  was  considerable.  Galileo 
then  informed  him  that  it  was  not  convenient  for  him  to 
travel  into  Egypt  or  Muscovy  in  order  to  try  the  experi- 
ment, but  that  if  the  adventurer  cared  to  do  so  himself,  he 
would  remain  in  Venice  and  let  him  try  to  converse  with 
him,  promising  that  if  the  experiment  were  a success  he 
would  become  the  purchaser.  It  need  hardly  be  said  that 
the  knave  preferred  to  try  his  fortune  elsewhere. 

Another  method  appears  to  have  been  much  believed 
in,  but  for  obvious  reasons  it  was  not  likely  to  be  often 
put  to  the  test  of  experiment.  It  consisted  in  cutting 
pieces  of  skin  from  corresponding  portions,  such  as  the 
arms,  of  two  persons,  and  mutually  transplanting  them, 
when  it  was  stated  that  each  transplanted  piece  would 
grow  to  the  new  arm,  which  is  quite  possible,  similar  oper- 
ations often  being  performed  in  modern  surgery.  The  rest 
of  the  story  however  makes  rather  large  demands  upon  our 
credulity.  The  transplanted  piece  of  skin  was  said  to  retain 
so  close  a sympathy  with  its  native  limb  as  to  be  sensitive 
to  any  injury  done  to  the  latter.  The  letters  of  the  alphabet 
were  to  be  tattooed  upon  the  transplanted  pieces  of  skin, 


THE  STORY  OF  THE  TELEGRAPH 


97 


and  whenever  either  member  of  the  pair  who  had  under- 
gone this  previous  preparation  wished  to  converse  with  his 
friend,  he  only  had  to  prick  the  letters  upon  his  arm  with 
a magnetic  needle,  so  as  to  spell  out  the  message,  and,  as 
each  letter  was  pricked  in  his  own  arm,  a corresponding 
pain  would  be  felt  in  that  of  his  friend. 

It  will  perhaps  appear  to  my  readers  almost  impossible 
that  any  reasonable  person  could  believe  such  statements, 
but,  foolish  as  they  appear  in  the  light  of  modern  knowl- 
edge, they  are  not  more  so  than  the  belief  in  the  efficacy 
of  electric  hair-brushes  and  magnetic  lockets — et  hoc  genus 
omne — which  not  many  years  ago  were  offered  for  sale  at 
almost  every  railway  station  in  London;  and  when  we  find 
such  absurdities  as  these  being  believed  in  by  the  masses, 
in  spite  of  our  present  standard  of  knowledge,  it  becomes 
easier  to  understand  how  even  learned  men  could  believe 
the  corresponding  nonsense  in  vogue  some  few  hundred 
years  ago,  when  the  standard  of  human  knowledge  was 
considerably  lower  than  it  is  at  present.  These  ideas 
moreover,  absurd  as  they  are,  are  not  without  interest,  as 
they  seem  to  foreshadow,  though  in  an  impossible  and 
ridiculous  fashion,  the  magnetic  telegraph  now  in  use 
throughout  the  civilized  world. 

The  electric  telegraph,  as  it  exists  to-day,  was  of  slow 
and  gradual  growth — so  slow  and  gradual  indeed  that  it  is 
impossible  to  point  to  any  one  man  as  being  the  inventor 
of  telegraphy. 

If  we  follow  the  history  of  any  scientific  invention  it  will 
always  be  found  that  the  process  of  development  resem- 
bles the  processes  of  nature  in  the  organic  world,  and  that 
though  it  may  appear  to  flash  suddenly  upon  the  world, 
as  Athene  was  said  to  have  sprung,  fully  armed,  from  the 


98 


ELECTRICITY  IN  MODERN  LIFE 


brain  of  Zeus,  this  sudden  appearance  is  really  only  the  ad- 
vance into  general  notice  of  the  results  of  long  and  patient 
but  unobtrusive  work;  and  just  as  the  classic  story  appears 
to  give  a perfect  analogue  to  the  sudden  appearance  of  a 
great  invention  in  the  public  field  of  view,  so  on  looking 
a little  closer  the  analogy  still  holds;  for  before  Athene 
sprang  from  the  head  of  Zeus  the  latter  had  swallowed 
her  mother  Metis. 

During  the  early  part  of  the  eighteenth  century  a good 
many  philosophers  occupied  themselves  with  experiments  in 
electricity,  concerning  themselves  chiefly  with  the  various 
means  of  producing  it  by  friction.  It  was  not,  however, 
until  the  year  1729  that  the  discovery  was  made  that  some 
bodies  conduct  electricity  freely  and  others  only  with  diffi- 
culty. This  discovery  of  the  fact  that  substances  can  be 
divided,  with  respect  to  their  electrical  behavior,  into  the 
two  great  classes  of  conductors  and  insulators,  was  made 
in  this  year  by  Stephen  Gray,  a pensioner  of  the  Charter- 
house, and  this  observation  was  of  such  prime  importance 
in  the  development  of  the  electric  telegraph  that  it  may 
almost  be  regarded  as  its  starting-point. 

A great  impetus  was  given  to  experimenting  in  electri- 
cal phenomena  by  Musschenbrdck’s  discovery  at  Leyden  in 
1745  of  what  is  now  known  as  the  Leyden  jar;  and  experi- 
ments on  the  transmission  of  electricity  which  had  been 
attempted  before  were  now  resumed  with  much  greater 
success. 

For  example,  in  April,  1746,  Abbd  Nollet  transmitted 
the  shock  of  a Leyden  jar  through  a number  of  Carthusian 
monks  joined  together  by  iron  wires,  and  forming  a circle 
five  thousand  four  hundred  feet  in  circumference.  The 
contortions  of  the  monks,  when  the  circuit  was  closed, 


THE  STORY  OF  THE  TELEGRAPH 


99 


were  accepted  as  sufficient  evidence  of  the  shock  having 
been  felt  throughout  the  whole  circuit,  and  the  fact  that 
these  contortions  took  place  simultaneously  showed  that  the 
time  occupied  by  the  electricity  in  traversing  the  circuit 
was  too  small  to  be  perceptible. 

The  first  actual  suggestion  of  an  electric  telegraph  was 
made  in  an  anonymous  letter  published  in  the  “Scots  Mag- 
azine” at  Edinburgh,  February  17,  1753.  The  letter  is 
initialled  “C.  M.,”  and  many  attempts  have  been  made  to 
discover  the  author’s  identity;  but  though  plausible  theo- 
ries have  not  been  wanting,  the  question  has  never  been  set 
at  rest,  and  a considerable  concurrence  of  evidence  indicates 
that  the  author’s  reason  for  concealing  his  identity  was  his 
fear  of  being  regarded  as  a magician  by  his  neighbors. 

The  suggestions  made  in  this  letter  were  that  a set 
of  twenty-six  wires  should  be  stretched  upon  insulated 
supports  between  the  two  places  which  it  was  desired  to 
put  in  connection,  and  at  each  end  of  every  wire  a metal- 
lic ball  was  to  be  suspended,  having  under  it  a letter  of  the 
alphabet  inscribed  upon  a piece  of  paper.  These  pieces  of 
paper  were  to  be  placed  upon  a horizontal  table,  at  distances 
of  about  an  inch  below  the  balls. 

Connection  was  to  be  effected  by  successively  bringing 
the  ends  of  the  wires  at  the  sending  station  into  contact  with 
the  charged  electrical  conductor,  in  such  an  order  as  to  spell 
out  the  message  which  was  to  be  sent,  and  the  message  was 
to  be  read  ofl:  at  the  receiving  station  by  observing  the  let- 
ters which  were  successively  attracted  by  their  correspond- 
ing balls,  as  soon  as  the  wires  attached  to  the  latter  received 
a charge  from  the  distant  conductor. 

In  1787  Monsieur  Lomond,  of  Paris,  made  the  very  im- 
portant step  of  reducing  the  twenty-six  wires  to  one,  and 


100 


ELECTRICITY  IN  MODERN  LIFE 


indicating  the  different  letters  by  various  combinations  of 
simple  movements  of  an  indicator,  consisting  of  a pith-ball 
suspended  by  means  of  a thread  from  a conductor  in  contact 
with  the  wire,  which  was  charged  by  being  put  in  contact 
with  a charged  electrified  conductor  at  the  other  end. 

In  the  year  1790  Chappe,  the  inventor  of  the  semaphore, 
or  optico-mechanical  telegraph,  which  was  in  practical  use 
previous  to  the  introduction  of  the  electric  telegraph,  de- 
vised a means  of  communication,  consisting  of  two  clocks 
regulated  so  that  the  second  hands  moved  in  unison,  and 
pointed  at  the  same  instant  to  the  same  figures,  which  were 
marked  round  the  dials. 

In  the  early  form  of  the  apparatus,  the  exact  moment 
at  which  the  observer  at  the  receiving  station  should  read 
off  the  figure  to  which  the  hand  pointed  was  indicated  by 
means  of  a sound  signal  produced  by  the  primitive  method 
of  striking  a copper  stew-pan,  but  the  inventor  soon  adopted 
the  plan  of  giving  electrical  signals  instead  of  sound  signals, 
hoping  in  this  way  to  be  able  to  employ  his  apparatus  for 
communicating  at  greater  distances  than  would  be  possible 
when  sound’ signals  were  used,  as  the  slow  rate  at  which 
sound  travels  would  make  the  interval  between  the  sending 
and  receiving  of  the  signal  so  great,  that  the  hand  of  the 
clock  at  the  receiving  station  would  in  the  meantime  have 
passed  on  to  some  other  figure  than  the  one  intended  to  be 
indicated.  He  therefore  used  a Leyden  jar  discharge  to  give 
a signal,  but  he  found  it  impossible,  when  the  distance  was 
at  all  considerable,  to  insulate  his  wires  sufficiently  well  to 
transmit  the  signals,  and  it  was  this  which  led  him  to  devise 
his  well-known  semaphore. 

It  was  this  difficulty  of  insulation  which  was  fatal  to  all 
the  telegraphic  systems  based  upon  the  use  of  electric  cur- 


THE  STORY  OF  THE  TELEGRAPH 


101 


rents  produced  by  frictional  machines,  or  by  the  discharge 
of  Leyden  jars. 

I pointed  out  in  an  earlier  chapter  that  the  electrical 
pressure,  or  electro-motive  force,  in  the  case  of  such  cur- 
rents is  extremely  high,  while  the  quantity  of  electricity 
transmitted  is  extremely  small,  so  that  in  order  to  transmit 
them  through  any  considerable  length  of  wire,  the  insulation 
must  be  exceedingly  good,  as  otherwise  the  leakage  would 
be  so  great  that  no  perceptible  quantity  would  reach  the  dis- 
tant end.  It  would  be  quite  impossible  practically  to  obtain 
the  insulation  required  for  a line  of  any  length,  but  it  is 
quite  a different  matter  for  the  telegraphs  actually  in  use, 
whether  the  currents  are  obtained  from  voltaic  batteries, 
or,  as  is  occasionally  done,  from  a small  magneto-dynamo 
machine,  for  in  this  case  a considerable  quantity  of  electric- 
ity is  transmitted  at  very  low  electrical  pressure,  and  there- 
fore on  the  one  hand  there  is  comparatively  little  tendency 
for  the  electricity  to  escape,  and  on  the  other  hand,  the 
quantity  of  electricity  being  large,  a certain  amount  of 
leakage  is  comparatively  unimportant. 

The  difference  between  the  two  cases  is  of  very  much  the 
same  character  as  that  between  conveying  water  in  a pipe 
three  or  four  feet  in  diameter,  with  a pressure  equivalent  to 
say  ten  feet  of  water,  and  carrying  it  through  a pipe  say  an 
eighth  of  an  inch  in  diameter,  with  a pressure  equivalent 
to  a height  of  several  thousand  feet  of  water.  It  is  easy  to 
see  that  in  the  second  case  the  pipe  would  have  to  be  enor- 
mously stronger  than  in  the  first,  and  that  all  the  water 
would  be  lost  if  even  a very  small  leakage  took  place,  while 
in  the  first  case  a considerably  greater  leakage  might  take 
place  without  producing  any  sensible  effect. 

In  1795  Don  Francisco  Salva  read  a paper  before  the 


102 


ELECTRICITY  IN  MODERN  LIFE 


Academy  of  Sciences  at  Barcelona  which  is  of  special  inter- 
est in  the  history  of  Telegraphy,  not  only  on  account  of 
the  extent  and  completeness  of  his  own  designs,  but  also  as 
foreshadowing  a good  deal  of  what  was  only  carried  out 
at  a much  later  date.  He  suggested,  in  the  first  place,  that 
instead  of  twenty-six  wires  being  used,  one  for  each  letter, 
six  or  eight  wires  only  should  be  employed,  each  charged 
by  a Leyden  jar,  and  that  different  letters  should  be  formed 
by  means  of  various  combinations  of  signals  from  these. 
So  far  this  was  no  advance  on  what  had  been  done  before, 
Lomond  having  already  shown  that  it  was  possible  to  con- 
vey the  signals  by  means  of  one  wire  only.  He  then,  how- 
ever, went  on  to  explain  that  it  would  be  exceedingly  diffi- 
cult to  maintain  even  this  number  of  wires  if  they  were  all 
separately  suspended  from  poles,  and  he  therefore  suggested 
that  they  should  be  separately  insulated,  and  then  rolled 
together  into  a single  cable,  which  is  exactly  what  is  done 
in  London  at  the  present  day. 

Salva  tells  us  that  in  his  first  trials  he  made  a cable  of 
this  kind  by  covering  the  wires  with  pitch-coated  paper, 
or  some  other  dielectric,  and  then  tying  them  together,  and 
binding  the  whole  with  paper. 

Salva  therefore  was  the  first  to  make  an  electric  tele- 
graph cable. 

He  also  suggested  that  this  cable  should  be  laid  in  sub- 
terranean tubes,  and  that,  in  order  to  improve  its  insulation, 
it  might  be  covered  with  one  or  two  coats  of  resin.  He  fur- 
ther pointed  out  that  the  intervention  of  the  sea -need  not 
prevent  telegraphic  communication  between  two  places,  for, 
as  he  tells  us,  it  is  not  impossible  to  construct  cables  imper- 
vious to  water,  and  to  lay  them  along  the  bottom  of  the  sea. 

In  the  experiments  by  which  Salva  illustrated  this  paper 


THE  STORY  OF  THE  TELEGRAPH  105 

he  did  not  adopt  his  own  suggestion  of  using  only  six  or 
eight  wires,  but  employed  seventeen  double  wires,  one  for 
each  essential  letter  of  the  alphabet,  those  which  are  little 
used  or  whose  power  could  be  represented  by  others  being 
omitted.  Designs  representing  each  of  these  letters  were 
formed  by  means  of  a number  of  separate  strips  of  tin-foil 
pasted  on  glass,  and  the  two  end  strips  of  each  letter  were 
attached  to  the  extremities  of  the  corresponding  pair  of 
wires.  A letter  was  indicated  by  taking  the  ends  of  the 
wires  belonging  to  it  and  connecting  them  with  the  two 
coatings  of  a charged  jar,  upon  which  the  observer  at  the 
distant  station  saw  the  letter  illuminated  by  the  spark  pass- 
ing across  the  breaks  in  the  tin-foil.  It  is  stated  that  this 
telegraph  was  actually  employed  over  a distance  of  about 
a kilometre,  the  outgoing  wires  being  all  collected  in  one 
cable  of  the  kind  described,  and  the  return  wires  in  a sec- 
ond. A number  of  other  attempts  were  made  during  the 
end  of  the  last  century  and  the  beginning  of  the  present 
one  to  devise  a practically  useful  system  of  telegraphic 
communication  by  means  of  frictionally  generated  currents 
of  electricity,  and  several  inventors  attempted  to  obtain  the 
assistance  of  the  Grovernment  in  carrying  out  their  projects, 
but  they  invariably  received  the  stereotyped  reply  that 
“telegraphs  of  any  kind  other  than  those  now  in  use  are 
entirely  unnecessary,  as  the  Government  are  fully  satisfied 
with  the  Semaphore  system.” 

I must  not,  however,  pass  from  this  branch  of  my  subject 
without  giving  some  account  of  the  work  of  Mr.  (afterward 
Sir  Francis)  Eonalds,  who  took  up  the  subject  of  telegraphy 
in  the  year  1816,  and  published  an  account  of  his  experi- 
ments in  1823,  in  a little  volume  entitled  “Description  of 
an  Electrical  Telegraph,  and  of  some  other  Electrical  Appa- 


104 


ELECTRICITY  IN  MODERN  LIFE 


Fig.  18. 


ratus,”  of  which  the  portion  relating  to  the  telegraph  was 
reprinted  in  1871. 

Eonalds  employed  a single  wire  of  brass  or  copper 

inclosed  in  thick  glass  tubes,  and 
laid  in  wooden  troughs  lined  inside 
and  out  with  pitch,  the  difierent 
lengths  of  glass  tubing  being  joined 
together  by  short  overlapping  tubes, 
sealed  with  wax,  in  order  to  exclude 
moisture. 

The  receiving  apparatus  con- 
sisted of  a circular  brass  plate, 
18,  divided  into  twenty  equal  parts,  and  rotated  by 
clockwork,  at  the  rate  of  one  complete  revolution  per  min- 
ute; each  division  carried  a figure,  a letter,  and  a prepara- 
tory sign.  The  figures  were  divided  into  two  series — each 

containing  the  numerals  from  one 
to  ten,  and  the  letters  were  ar- 
ranged alphabetically,  leaving  out 
J,  Q,  U,  W,  X,  Z. 

In  front  of  this  plate  was  fixed 
a second  disk  of  the  same  size,  pro- 
vided with  an  aperture  as  shown 
in  Fig.  19,  and  this  disk  could  be 
turned  by  hand  about  its  centre. 
Fig.  19.  which  coincided  with  the  first  disk. 


Fig. 


The  aperture  shown  in  the  illustration  was  of  such  a size 
as  only  to  allow  one  letter  with  its  corresponding  figure  and 
preparatory  sign  to  be  visible  at  any  one  time.  An  electro- 
scope, consisting  of  a pair  of  pith-balls  attached  by  means 
of  threads  to  a metal  support  in  connection  with  the  line- 
wire,  was  suspended  in  front  of  the  latter  disk. 


THE  STORY  OF  THE  TELEGRAPH 


105 


The  transmitting  apparatus  consisted  simply  of  a small 
cylinder  electrical  machine,  the  prime  conductor  of  which 
was  in  connection  with  the  metal  conductor  from  which  the 
pith-balls  were  suspended,  and  through  that  with  the  line- 
wire.  The  transmitter  and  receiver  at  each  station  were 
exactly  similar.  When  it  was  desired  to  send  a message 
from  either  end,  the  outer  disk  was  turned  so  as  to  exhibit 
the  letter  A with  its  corresponding  numeral  and  preparatory 
sign,  which,  in  this  case,  stood  for  the  word  “prepare.” 

The  clock  was  then  started,  and  a signal  sent  along  the 
wire  every  time  that  the  sign  “prepare”  came  opposite  to 
the  aperture.  The  person  at  the  receiving  station  in  the 
meantime  adjusted  his  apparatus  so  that  the  letter  A was 
shown  by  his  receiver  at  the  moment  when  the  signal 
“prepare”  was  sent  through  the  wire,  and,  as  soon  as  this 
had  been  done,  he  signalled  the  fact  by  sending  a discharge 
at  the  moment  that  the  preparatory  signal  standing  for  the 
word  “ready”  appeared  opposite  the  aperture  of  his  in- 
strument. In  this  way  the  two  dials  were  made  to  show 
the  same  letter  simultaneously. 

Ronalds  drew  up  a sort  of  telegraphic  code  by  which 
words,  and  sometimes  even  complete  sentences,  could  be 
transmitted  by  only  three  discharges,  and,  in  order  to  show 
whether  letters,  figures,  or  code-figures,  referring  to  words 
and  sentences  in  the  dictionary,  were  intended,  certain  pre- 
paratory signs  were  made  beforehand,  such  as  “note- 
letters,”  “note-figures,”  “dictionary.”  Whenever  a pre- 
paratory sign  was  to  be  read  instead  of  a letter  or  figure, 
the  fact  was  announced  by  sending  an  extra  strong  charge 
through  the  line,  thus  causing  the  pith-balls  to  diverge  more 
widely  than  usual.  In  order  to  obviate  the  necessity  of 
continually  watching  the  instrument  at  each  station,  a small 


106 


ELECTRICITY  IN  MODERN  LIFE 


Volta  cannon  was  provided,  consisting  of  a tube  having 
its  open  end  closed  by  a cork,  and  containing  an  explosive 
mixture  of  oxygen  and  hydrogen  gases.  A pair  of  wires 
in  connection  with  the  direct  and  return  wires  of  the  line 
passed  through  apertures  in  this  tube,  and  came  very  close 
together  without  touching,  inside  it,  so  that  when  a dis- 


Fig.  20. 


charge  was  sent  through  the  line  from  the  distant  station, 
the  gas  was  exploded,  and,  by  its  report,  called  the  attention 
of  the  observer  at  that  station. 

The  whole  apparatus  is  shown  in  Fig.  20,  D being  the 
electrical  machine,  B the  pith-ball  electroscope,  A the  screen 
with  its  orifice,  F the  V olta  pistol,  and  E the  tube  contain- 
ing the  conducting  wires. 


THE  STORY  OF  THE  TELEGRAPH 


107 


In  the  work  previously  referred  to,  Eonalds  proposed 
that  telegraph  offices  should  be  established  throughout  the 
kingdom.  “Why,’’  he  says,  “has  no  serious  trial  yet  been 
made  of  the  qualifications  of  so  diligent  a courier  ? and,  if 
he  should  be  proved  competent  to  the  task,  why  should  not 
our  kings  hold  counsels  at  Brighton  with  their  ministers 
in  London?  Why  should  not  our  government  govern  at 
Portsmouth  almost  as  promptly  as  in  Downing  Street? 
Why  should  our  defaulters  escape  by  the  default  of  our 
foggy  climate?  and,  since  our  piteous  inamorati  are  not 
Alphei,  why  should  they  add  to  the  torments  of  absence 
those  dilatory  torments,  pens,  ink,  paper,  and  posts  ? Let 
us  have  electrical  conversazione  offices  communicating  with 
each  other  all  over  the  kingdom  if  we  can.  ’ ’ 

It  would  .have  been  pretty  well  impossible  to  have  made 
a more  accurate  forecast  of  the  part  now  played  by  the  elec- 
tric telegraph  in  our  daily  life.  The  diSerent  residences  of 
her  Majesty  are  connected  by  telegraph  wires  with  the  gov- 
ernment offices  in  Downing  Street,  and  ministers  can  com- 
municate with  their  subordinates,  or  be  recalled  upon  occa- 
sions of  emergency,  from  any  part  of  the  kingdom  or  from 
abroad.  The  telegraph  has  become  one  of  the  most  efficient 
aids  to  the  detective  police  force,  and  many  a time  has  it 
happened  that  a thief  or  a murderer  has  succeeded  in  getting 
into  a train  for  some  distant  seaport  on  his  way  to  America 
or  elsewhere,  only  to  be  stopped  on  arriving  at  his  destina- 
tion by  detectives  who  had  received  his  exact  description 
by  telegraph.  If  the  criminal  succeeds  in  getting  out  of 
the  country,  even  if  he  goes  as  far  as  the  Antipodes,  he  will 
generally  find  on  arriving  there  that  his  description  has  pre- 
ceded him,  and  he  may  not  improbably  be  actually  met  on 
landing  by  the  local  police,  who  have  received  by  telegraph 


108 


ELECTRICITY  IN  MODERN  LIFE 


a complete  description  of  him,  together  with  the  name  of 
the  ship  in  which  he  sailed.  With  regard  to  the  “piteous 
inamorati,”  the  post-office  officials,  if  it  were  not  for  the 
regulation  which  compels  them  to  maintain  absolute  reti- 
cence about  the  contents  of  all  telegrams  passing  through 
their  hands,  would  have  amusing  and  sometimes  pathetic 
accounts  to  give  of  the  numerous  messages  which  they  have 
to  transmit  from  love-sick  swains  and  forlorn  lasses. 

The  underground  cable  employed  by  Ronalds  was  not 
so  very  different  from  those  which  are  now  in  use,  though 
the  India-rubber  and  gutta-percha*  now  used  as  insulators 
are  a great  improvement  on  the  glass  tubes  employed  by 
him.  Ronalds,  however,  pointed  out  that  pitch  and  cloth 
might  be  employed  as  insulators,  as  had  already  been  sug- 
gested by  Oavallo;  and  tarred  tape  is  still  very  largely  em- 
ployed, on  the  score  of  cheapness,  where  very  high  insula- 
tion is  not  required. 

Ronalds,  moreover,  pointed  out  that  cast-iron  troughs 
might  be  made  as  tight  as  gas  pipes  if  it  were  considered 
desirable  to  employ  them,  and  the  system  of  laying  insu- 
lated telegraph  wires  in  cast-iron  pipes  is  one  which  is  very 
extensively  employed  by  the  Post-Office  at  the  present  time 
in  London.  The  tubes  are  usually  laid  down  under  the 
pavement,  with  openings  at  intervals,  closed  by  movable 
covers,  to  enable  defective  wires  to  be  removed,  and  new 
ones  drawn  in  when  required,  without  taking  up  the  pipes. 

Ronalds’s  remarks  regarding  the  question  of  preserving 
the  wires  against  malicious  injury  are  so  sensible  and  witty 
as  to  be  worth  quoting  in  full.  “To  protect  the  wires,’'  he 
says,  “from  mischievously-disposed  persons,  let  the  two 
tubes  be  buried  six  feet  below  the  surface  of  the  middle 
of  highroads,  and  let  each  tube  take  a different  route  to 


THE  STORY  OF  THE  TELEGRAPH 


109 


arrive  at  the  same  place.  Could  any  number  of  rogues 
then  open  trenches  six  feet  deep  in  two  or  more  public  high- 
roads or  streets,  and  get  through  two  or  more  strong  cast- 
iron  troughs  in  a less  space  of  time  than  forty  minutes? 
For  we  shall  presently  see  that  they  would  be  detected 
before  the  expiration  of  that  time.  If  they  could,  render 
their  difliculties  greater  by  cutting  the  trench  deeper,  and 
should  they  still  succeed  in  breaking  the  communication 
by  these  means,  hang  them  if  you  can  catch  them,  damn 
them  if  you  cannot,  and  mend  it  immediately  in  both  cases. 
Should  mischievous  devils  from  the  subterranean  regions 
attack  my  wire,  condemn  the  houses  belonging  thereunto, 
which  cannot  easily  escape  detection  by  running  away.” 

Eonalds  proposed,  moreover,  in  order  that  any  breakage, 
whether  accidental  or  otherwise,  in  the  line  might  be  imme- 
diately detected,  to  keep  the  line  wire  constantly  charged 
with  electricity,  and  to  have  certain  testing  stations  estab- 
lished at  convenient  positions  along  the  line,  at  which  tests 
should  be  made  at  short  intervals.  This  idea  is  almost 
exactly  carried  out  in  the  telegraphs  of  the  present  day, 
except  that  Voltaic  batteries  are  used  instead  of  frictional 
machines  to  supply  the  current,  and  it  is  unnecessary  al- 
ways to  keep  the  battery  in  circuit,  the  current  only  having 
to  be  turned  on  while  the  test  is  actually  being  made. 

I must  make  one  more  quotation  from  Eonalds’s  work,  as 
it  shows  that  his  insight  into  electrical  phenomena  enabled 
him  to  forecast  a difficulty  in  the  transmission  of  signals 
through  long  underground  cables  which  no  one  else  seems 
to  have  thought  of — a difficulty  which,  in  the  early  days  of 
submarine  telegraphy,  proved  to  be  a formidable  obstacle 
in  the  way  of  the  rapid  transmission  of  signals  through  long 
submerged  cables,  and  which  was  first  explained  with  the 


110 


ELECTRICITY  IN  MODERN  LIFE 


aid  of  mathematical  analysis  by  Sir  W.  Thomson,  and  prac- 
tically remedied  by  the  beautiful  signalling  apparatus  which 
he  devised  in  accordance  with  the  requirements  indicated 
by  theory. 

Ronalds’s  statement  is  as  follows:  ‘‘That  objection 
which  has  seemed  to  most  of  those  with  whom  I have 
conversed  on  the  subject  the  least  obvious,  appears  to  me 
the  most  important,  therefore  I begin  with  it,  viz.,  the 
probability  that  the  electrical  compensation  which  would 
take  place  in  a wire  inclosed  in  glass  tubes  of  many  miles 
in  length  (the  wire  acting,  as  it  were,  like  the  interior  coat- 
ing of  a battery)  might  amount  to  the  retention  of  a charge, 
or,  at  least,  might  destroy  the  suddenness  of  a discharge, 
or  in  other  words,  it  might  arrive  at  such  a degree  as  to 
retain  the  charge  with  more  or  less  force,  even  although 
the  wire  were  brought  into  contact  with  the  earth.” 

Ronalds  completely  proved  the  practicability  of  his  plan, 
not  only  on  the  short  underground  line  which  I have  de- 
scribed, but  also  upon  an  overhead  line  some  eight  miles 
in  length,  constructed  by  carrying  a telegraph  wire  back- 
ward and  forward  over  a wooden  framework  erected  in  his 
garden  at  Hammersmith;  and  although,  when  the  electro- 
magnetic telegraph  came  into  use,  he  freely  admitted  the 
great  superiority  of  electro-magnetism  for  telegraphic  pur- 
poses, yet  he  maintained  to  the  last  that  if  his  own  system 
had  been  tried  on  a large  scale  it  would  have  been  a prac- 
ticable one,  even  for  lines  of  many  miles  in  length. 

The  first  attempt  to  employ  Voltaic  electricity  in  teleg- 
raphy was  made  by  Don  Francisco  Salva,  whose  frictional 
telegraph  has  already  been  referred  to.  On  the  14th  of 
May,  1800,  Salva  read  a paper  on  “Galvanism  and  Its  Ap- 
plication to  Telegraphy”  before  the  Academy  of  Sciences 


THE  STORY  OF  THE  TELEGRAPH 


111 


at  Barcelona,  in  which  he  described  a number  of  experi- 
ments which  he  had  made  in  telegraphing  over  a line  some 
310  metres  in  length.  In  these  experiments  he  made  use  of 
Galvani’s  discovery  of  the  convulsions  produced  in  a frog’s 
leg  by  means  of  electrical  discharges,  the  motion  of  the 
frog’s  leg  being  employed  to  indicate  the  signals.  In  the 
course  of  these  experiments,  Salva  discovered  that  the  frogs 
at  the  distant  station  were  sometimes  thrown  into  convul- 
sions, even  when  no  frictional  discharge  was  passing  along 
the  line,  and  he  soon  found  that  this  was  due  to  the  slight 
Voltaic  current  generated  by  the  contact  between  the  frogs 
and  the  conducting  wires  at  the  sending  station.  This  ap- 
pears to  have  been  the  first  discovery  of  the  fact  that  the 
Voltaic  current  might  be  employed  for  the  transmission 
of  messages. 

Salva  continued  his  experiments  in  this  direction,  ob- 
taining the  electricity  from  a large  number  of  frogs,  and 
a few  years  later  he  applied  the  then  recent  discovery  of 
the  Voltaic  pile  to  the  same  purpose,  the  liberation  of  bub- 
bles of  gas  by  the  decomposition  of  water  at  the  receiving 
station  being  the  method  adopted  for  indicating  the  passage 
of  the  signals. 

A telegraph  of  a very  similar  character  was  devised 
by  Sdmmering,  and  described  in  a paper  communicated  by 
the  inventor  to  the  Munich  Academy  of  Sciences  in  1809. 
Sdmmering  used  a set  of  thirty-five  wires  corresponding 
to  the  twenty-five  letters  of  the  German  alphabet  and  the 
ten  numerals. 

These  wires  were  connected  to  thirty-five  gold  points 
or  pins  which  passed  up  through  the  bottom  of  a trough 
of  water,  and  the  letters  and  figures  were  indicated  by 
connecting  the  terminals  of  the  Voltaic  pile  to  different 


112 


ELECTRICITY  IN  MODERN  LIFE 


pairs  of  wires,  when  bubbles  of  oxygen  and  hydrogen 
respectively  were  evolved  from  the  corresponding  gold 
terminals. 

In  order  to  attract  attention  at  the  distant  station,  the 
gas  rising  in  bubbles  from  two  contiguous  pins  was  allowed 
to  collect  under  an  inverted  glass  cup  attached  to  the  end 
of  a long  lever,  and  this  lever,  rising  as  the  gas  was  liber- 
ated, caused  a second  lever  to  descend  and  throw  oflE  a 
small  leaden  ball  resting  upon  it,  which  in  falling  set  the 
clockwork  of  an  ordinary  alarm  in  motion. 

Oersted’s  discovery  of  the  action  of  the  electric  current 
upon  a suspended  magnetic  needle  provided  a new  and 
much  more  hopeful  method  of  applying  the  electric  cur- 
rent to  telegraphy.  The  great  French  astronomer  Laplace 
appears  to  have  been  the  first  to  suggest  this  application  of 
Oersted’s  discovery,  and  he  was  followed  shortly  afterward 
by  Ampere,  who  in  the  year  1820  read  a paper  before  the 
Paris  Academy  of  Sciences,  in  the  course  of  which  he 
sketched  out  the  plan  of  a telegraph  in  which  the  signals 
were  to  be  indicated  by  small  magnets  placed  under  the 
wires. 

In  1829  Professor  Fechner,  of  Leipsic,  pointed  out  that 
the  effect  at  the  distant  station  might  be  increased  by 
inclosing  the  needles  in  coils  consisting  of  many  turns 
of  wire,  as  Schweigger  had  already  done  in  constructing 
his  galvanometer. 

In  the  following  year  Professor  Ritchie,  of  the  Royal 
Institution  of  London,  adopted  this  suggestion  and  ex- 
hibited a model  telegraph  in  which  twenty-six  separate 
circuits  were  employed  with  twenty-six  suspended  mag- 
netic needles,  each  surrounded  by  a coil  of  wire.  A much 
more  practical  form  of  telegraph  was  invented  soon  after 


THE  STORY  OF  THE  TELEGRAPH 


113 


this  by  Baron  Pawel  Lwowitch  Schilling.  Baron  Schil- 
ling’s attention  was  first  directed  to  telegraphy  by  seeing 
Sommering’s  telegraph  in  action  in  1810  at  Munich,  Schil- 
ling being  one  of  the  attaches  of  the  Eussian  Embassy  at 
that  place.  Schilling’s  first  electrical  experiments  were 
directed  to  the  use  of  electricity  for  the  purposes  of  war, 
and  consisted  of  attempts  to  provide  telegraphic  commu- 
nication between  fortified  places,  and  to  explode  powder 
mines  at  a distance  by  means  of  electric  discharges  carried 
through  insulated  wires  laid  under  ground  or  under  water. 

The  final  form  of  Schilling’s  telegraph  required  a single 
metallic  circuit  only,  consisting  of  a direct  and  return  wire. 
The  sending  instrument  was  simply  a key  to  make  and 
break  contact,  or  to  reverse  the  current  through  the  line. 
The  receiving  instrument  consisted  of  a galvanometer 
formed  of  a magnetized  needle,  suspended,  by  means 
of  a silk  fibre,  within  a coil  of  wire  in  circuit  with 
the  line,  the  motions  of  the  needle  being  indicated  by 
means  of  a small  disk  of  paper  attached  to  the  suspended 
fibre  parallel  to  the  needle,  and  painted  white  on  one  side 
and  black  on  the  other.  In  this  way  either  the  white  or 
the  black  face  was  brought  opposite  the  observer,  accord- 
ing to  the  direction  in  which  the  current  was  sent  through 
the  line,  and  the  different  letters  and  other  signs  were  in- 
dicated by  means  of  various  combinations  of  these  two 
primary  signals,  for  example,  writing  W for  white  and 
B for  black;  the  vowels  were  indicated  by  the  following 
combinations — A— bw,  E = b,  I=:bb,  0 = bwb,  U^wwb. 

The  first  bi-signal  alphabet  is  popularly  supposed  to 
have  been  devised  by  Morse,  but  as  a matter  of  fact  such 
alphabets  were  employed  for  signalling  purposes  as  far  back 
as  the  times  of  the  ancient  Greeks  and  Eornans,  the  signals 


114 


ELECTRICITY  IN  MODERN  LIFE 


consisting  generally  either  of  sounds,  or  signs  visible  at  a 
distance.  Schilling’s  device  for  attracting  the  attention 
of  the  observer  at  the  distant  station  was  very  similar  to 
that  of  Sdmmering,  upon  which  it  was  founded.  The  silk 
fibre  by  which  the  needle  was  suspended  was  replaced  by 
a rigid  metal  wire  carrying  a horizontal  metal  arm,  and 
when  the  needle  was  deflected  by  the  current  this  arm  struck 
against  a delicately  balanced  lever,  and  caused  a leaden  ball 
resting  on  it  to  fall  upon  a second  lever  and  set  a clockwork 
alarm  in  motion,  as  in  Sdmmering’s  instrument.  Schilling’s 
telegraph  is  of  special  interest  owing  to  its  being  the  proto- 
type of  the  modern  needle  telegraph  instrument,  and  also 
because  it  was  the  immediate  cause  of  the  electric  telegraph 
being  introduced  into  England. 

In  1883  a telegraph  was  constructed  by  Grauss  and  Weber 
at  Gottingen  for  transmitting  signals  between  their  magnetic 
observatory  and  the  physical  laboratory  of  the  University. 
This  telegraph  is  principally  of  interest  on  account  of  the 
simple  and  ingenious  method  employed  for  increasing 
the  sensibility  of  the  receiving  instrument,  the  plan  being  the 
same  that  was  afterward  adopted  by  Sir  W.  Thomson  in  his 
“Mirror”  galvanometer. 

The  current  was  generated  by  an  ordinary  voltaic  battery 
until  the  year  1835,  after  which  a magneto-electric  machine, 
made  by  Steinheil,  was  employed.  The  current  produced 
by  the  magneto  machine  was  made  to  deflect  a large  sus- 
pended magnet  weighing  about  one  hundred  pounds,  and  as 
the  deflections  of  this  magnet  were  exceedingly  small,  they 
were  observed  by  attaching  a mirror  to  the  magnet,  and  the 
deflections  were  read  by  placing,  at  a distance  of  ten  or 
twelve  feet,  a telescope,  at  the  top  of  which  was  fixed 
a horizontal  scale,  the  reflection  of  the  scale  in  the  mirror 


THE  STORY  OF  THE  TELEGRAPH 


115 


attached  to  the  magnet  being  read  off  through  the  telescope. 
A “bi-signal”  alphabet  very  similar  to  that  of  Schilling’s 
was  employed.  The  primary  signals  consisted  of  deflections 
of  the  magnet  and  mirror  to  the  right  and  left  respectively. 
Some  kind  of  alarm  was  employed  in  connection  with  this 
telegraph,  but  the  details  of  its  construction  have  not  been 
preserved. 

Gauss  believed  that  this  telegraph  was  capable  of  being 
brought  into  a practical  form  suitable  for  general  telegraphic 
purposes,  but  not  being  able  to  spare  time  from  his  scientific 
investigations  to  devote  himself  to  the  practical  working  out 
of  the  subject,  .he  invited  Steinheil  to  take  it  up,  and  this 
inventor  introduced  a number  of  modifications  which  vastly 
improved  the  original  instruments  of  Gauss  and  Weber. 
In  order  to  provide  the  current  Steinheil  employed  a 
magneto-generator,  consisting  of  a permanent  compound 
magnet  built  up  of  seventeen  horseshoe  bars  of  magnetized 
steel,  with  a pair  of  coils,  consisting  of  fifteen  thousand 
turns  of  fine  silk-covered  wire,  which  were  made  to  rotate 
between  the  poles,  a commutator  being  provided  to  make 
the  current  continuous  in  direction.  The  coils  were  set  in 
motion  by  means  of  a fly-bar  terminating  in  two  metal  balls 
attached  at  right  angles  to  the  axis,  about  which  they 
rotated.  The  receiving  instrument  consisted  of  a pair  of 
magnets,  to  which  were  attached  two  cups,  terminating 
below  in  fine  perforated  beaks,  and  filled  with  printing  ink, 
so  that  each  time  the  magnets,  with  the  cups  attached  to 
them,  were  depressed,  a dot  was  made  upon  a strip  of  paper 
carried  under  the  cups  by  means  of  clockwork.  The  con- 
nections were  made  in  such  a manner  that  one  of  these 
magnets  was  depressed  when  the  fly-bar  made  half  a turn 
from  right  to  left,  and  the  other  one  when  it  made  half  a 


116 


ELECTRICITY  IN  MODERN  LIFE 


turn  from  left  to  right.  In  some  of  Steinheil’s  receiving 
instruments  the  magnets,  instead  of  being  provided  with 
cups,  were  made  to  strike  upon  two  bells  of  different  tones, 
so  that  Steinheil  was  the  original  inventor  both  of  “printing 
telegraphs”  and  of  “sounder  receivers.” 

In  the  year  1838  Steinheil  made,  accidentally,  the  very 
important  discovery  that  the  return  wire  might  be  dispensed 
with,  and  the  earth  used  to  complete  the  circuit,  so  that 
only  a single  wire  was  necessary  in  order  to  effect  communi- 
cation between  two  stations. 

Gauss  had  suggested  that  the  two  rails  of  a railway 
line  might  be  employed  as  the  conductors  of  a tele- 
graph line,  and  in  July,  1838,  Steinheil  tried  the  experi- 
ment on  the  railway  between  Nuremberg  and  Furth,  but 
he  was  unable  to  insulate  the  rails  sufficiently  to  transmit 
the  current. 

In  making  these  experiments  the  great  conducting  power 
of  the  earth  impressed  itself  forcibly  upon  his  mind,  and 
suggested  to  him  that  it  might  possibly  be  employed  instead 
of  the  return  wire,  and  he  lost  no  time  in  putting  the  idea 
to  the  test  of  experiment.  It  was  perfectly  successful,  and 
formed  one  of  the  greatest  improvements  in  electric  teleg- 
raphy, owing  to  the  great  reduction  which  it  effected  in 
the  cost  of  erecting  telegraph  lines. 

The  next  important  step  in  the  development  of  the  elec- 
tric telegraph  was  made  by  an  Englishman,  Edward  Davy. 
It  would  take  up  too  much  space  to  give  a detailed  descrip- 
tion of  Davy’s  telegraph,  as  his  system  was  developed  with- 
out any  knowledge  of  what  other  workers  in  the  same  field 
had  been  doing,  and  was  consequently  one  of  considerable 
complication.  Two  of  his  inventions,  however,  must  not 
be  passed  over  without  notice — viz.,  the  “Eelay”  and  the 


THE  STORY  OF  THE  TELEGRAPH 


117 


“Chemical  Eecording  Telegraph,”  as  they  form  important 
landmarks  in  the  story  of  the  telegraph. 

The  principle  of  the  “Eelay,”  or,  as  Davy  called  it,  the 
“Electrical  Eenewer,  ” though  extremely  simple,  is  one  of 
very  great  importance,  as  it  greatly  reduced  the  difficulties 
incidental  to  long-distance  telegraphy.  The  object  of  the 
relay  is  to  obviate  the  necessity  of  using  very  large  currents 
to  compensate  for  the  leakage  inevitable  in  the  case  of  long 
lines.  The  principle  of  the  method  consists  in  breaking 
up  a long  circuit  between  two  distant  stations  into  a series 
of  shorter  circuits,  each  complete  in  itself.  Between  each  of 
these  circuits  is  placed  a relay,  which  is  simply  an  appa- 
ratus, which,  when  a signal  is  sent  from  the  transmitting 
station,  makes  connection  between  the  next  circuit  beyond 
it  and  a local  battery,  and  thus  automatically  carries  on 
the  signal. 

In  Davy’s  first  relay  the  further  end  of  the  first  line  wire 
terminated  in  a rectangular  figure  of  8 coil  fixed  in  a hori- 
zontal position.  Within  each  coil  was  placed  a needle, 
balanced  upon  a horizontal  axis,  and  stops  were  placed  to 
prevent  each  of  the  needles  from  moving,  except  in  one 
direction.  When  a current  was  sent  through  the  line,  one  or 
other  of  the  needles  was  deflected,  according  to  the  direction 
of  the  current.  The  lower  end  of  each  needle  carried  a cross 
piece  of  copper  wire,  with  its  ends  turned  downward.  One 
of  these  ends  was  always  immersed  in  a cup  of  mercury, 
which  was  in  connection  with  one  of  the  terminals  of  a gal- 
vanic battery,  and  the  other  end  was  made  to  dip  into  a 
second  mercury  cup  whenever  the  needle  was  deflected 
by  a current  through  the  coil.  This  second  cup  formed 
one  of  the  terminals  of  the  next  circuit,  which  was  in  this 
manner  put  in  connection  with  the  battery. 


118 


ELECTRICITY  IN  MODERN  LIFE 


In  Davy’s  chemical  recording  telegraph,  a strip  of  calico 
impregnated  with  Iodide  of  Potassium  and  Chloride  of 
Lime  passed  over  a copper  cylinder,  and  was  carried  onward 
when  the  cylinder  revolved.  When  a signal,  was  sent  from 
the  transmitting  station,  a metallic  contact  piece,  forming 
one  of  the  terminals  of  the  line,  was  made  to  press  against 
the  calico,  which  completed  the  circuit  through  the  latter 
and  the  metallic  cylinder  over  which  it  passed.  Every  time 
that  a current  was  sent  through  the  calico  a mark  was  made 
upon  it  by  the  chemical  decomposition  of  the  salts  with 
which  it  was  impregnated,  thus  giving  a permanent  record 
of  the  signal.  The  metal  cylinder  was  not  made  to  revolve 
continuously,  but,  by  means  of  a mechanism  set  in  motion 
by  the  transmitting  current,  it  was  made  to  advance  through 
a certain  space  after  the  transmission  of  every  signal. 

In  the  year  1834,  Professor  Wheatstone,  a physicist  of 
great  eminence,  was  engaged  in  researches  on  the  velocity 
of  electric  waves  in  solid  conductors,  and  these  experiments 
appear  to  have  first  directed  his  attention  to  the  subject  of 
electric  telegraphy,  in  the  development  of  which  he  played 
an  important  part.  Very  shortly  after  Wheatstone  turned 
his  attention  to  the  subject  of  telegraphy,  he  associated  with 
himself  a Mr.  Cooke,  who  had  already  been  engaged  in 
the  construction  of  telegraph  lines  for  railway  purposes. 
Henceforth  the  two  inventors  worked  together,  and  their 
labors  are  of  special  interest  and  importance,  not  only  on 
account  of  the  actual  improvements  which  they  effected, 
but  because  they  were  the  first  to  establish  the  telegraph 
for  practical  purposes  on  a comparatively  large  scale,  thus 
bringing  it  into  much  closer  touch  with  the  public  than 
while  it  was  confined  to  laboratory  experiments,  or  to  effect- 
ing scientific  communications  on  a small  scale,  as  in  the  case 


THE  STORY  OF  THE  TELEGRAPH 


119 


of  Gauss  and  Weber’s  telegraph  perfected  by  Steinheil. 
The  first  joint  invention  of  Wheatstone  and  Cooke  consisted 
of  a telegraph  with  five  indicators  and  as  many  line  wires. 
Its  details  were  very  carefully  worked  out,  but  practically 
it  was  inferior  to  that  of  Steinheil,  and  though  it  had  a fair 
trial  on  the  Great  W estern,  and  on  the  London  and  Birming- 
ham Railways,  it  had  to  be  given  up  on  account  of  its  heavy 
expense,  due  to  the  large  number  of  line  wires  employed. 

Wheatstone  was  the  first  to  contrive  a really  practical 


Fig.  21. 


alarm  for  calling  the  attention  of  the  observer  at  the  receiv- 
ing station.  The  arrangement  of  this  instrument  is  shown 
in  Fig.  21.  It  consisted  of  a clockwork  alarm,  previously 
wound  up,  and  prevented  from  running  down  by  means  of 
a toothed  wheel  n resting  against  a lever  p,  the  lower  end 
V of  which  was  made  of  soft  iron,  and  formed  the  armature 
of  the  electro-magnet  U.  When  a current  was  sent  through 
the  coil  U the  armature  V was  attracted,  releasing  the 
wheel  and  allowing  the  bell  of  the  alarm  to  ring.  The 

electro -magnet  was  placed  in  circuit  w’ith  the  line  in  the 

Science — Vol.  XIII — 6 


120 


ELECTRICITY  IN  MODERN  LIFE 


manner  indicated  in  the  diagram,  where  1 and  2 are 
the  direct  and  return  wires  of  the  line,  K is  a battery, 
and  5 is  a key  consisting  of  two  metal  springs  a,  6,  separated 
by  a strip  of  ivory,  the  lower  one  b being  mounted  on  a 
block  of  wood.  The  circuit  was  completed,  and  the  alarm 
set  in  motion,  by  depressing  the  spring  a so  as  -to  bring 
it  in  contact  with  b,  Wheatstone,  like  Davy,  experienced 
the  difficulty  of  the  weakening  of  the  current  by  the  resistance 
of  the  line  and  apparatus,  and  by  leakage,  due  to  imperfect 
insulation,  and  he  remedied  it  in  a similar  manner  by  means 
of  a relay  which  introduced  a local  battery  into  the  circuit. 

Another  inventor  whose  name  is  now  well  known  in  te- 
legraphy was  Morse,  an  American  artist,  who  is  said  to  have 
first  conceived  the  idea  of  an  electro-chemical  telegraph  in 
the  year  1832  while  on  his  homeward  voyage  from  Europe. 
He  received  considerable  assistance  in  his  first  attempts  in 
this  direction,  and  also  in  his  subsequent  experiments,  from 
a fellow-passenger — Dr.  Jackson,  of  Boston — who  had  a con- 
siderable acquaintance  with  electricity  and  chemistry,  and 
who  had  seen  a good  many  experiments  in  telegraphy  carried 
out  in  Paris.  In  the  first  apparatus  constructed  by  Morse, 
the  signals  were  recorded  by  passing  the  current,  by  means 
of  platinum  contact  points,  through  paper  moistened  with 
acetate  or  carbonate  of  lead;  or  impregnated  with  turmeric, 
and  moistened  with  a solution  of  sulphate  of  soda. 

The  subject  of  electric  telegraphy  had  by  this  time 
attracted  the  attention  of  numerous  scientific  and  practical 
men,  but  space  will  not  allow  of  my  discussing  in  detail 
their  various  contributions  to  the  subject;  I will  therefore 
conclude  the  story  of  the  telegraph  at  this  point,  reserving 
for  the  next  chapter  the  description  of  the  more  important 
telegraphic  apparatus  now  in  use. 


OVERLAND  TELEGRAPHS 


121 


CHAPTER  X 

OVERLAND  TELEGRAPHS 

WHEATSTONE  AND  COOKE’S  SINGLE-NEEDLE  TELE- 
GRAPH.— In  this  instrument  the  letters  of  the 
alphabet  are  indicated  by  motions  to  right  or 
left  of  a small  pointer  or  needle  capable  of  moving  a short 
distance  between  two  fixed  stops.  The  pointer,  with  its  dial 
and  the  signs  corresponding 
to  each  letter,  is  shown  in 
Fig.  22;  the  two  stops  are 
shown  in  the  diagram  on 
either  side  of  the  upper  por- 
tion of  the  needle.  In  the 
first  instrument  made  by 
Wheatstone  and  Cooke  five 
needles  or  pointers  were  em- 
ployed, which  were  afterward 
reduced  to  two,  and  finally  to  fig.  22. 

one.  A few  double-needle  instruments  are  still  in  use 
on  some  of  our  railways,  but  they  are  rapidly  being  re- 
placed by  single-needle  instruments,  which  are  much  more 
convenient. 

The  construction  of  the  single-needle  instrument  is 
shown  in  the  accompanying  diagrams.  Fig.  23  shows 


122 


ELECTRICITY  IN  MODERN  LIFE 


a front  view  of  the  instrument  with  the  cover  and  dial 
removed.  Fig.  24  shows  a side  view  of  the  interior,  and 
Fig.  25  shows  a horizontal  section  of  the  commutator,  or 


Fig.  25. 


sending  arrangement.  Corresponding  parts  are  indicated 
by  the  same  letters  in  all  the  three  diagrams. 

The  upper  portion  of  the  apparatus,  marked  A in  Fig. 


OVERLAND  TELEGRAPHS 


123 


23,  is  the  receiver.  It  is  formed  of  two  ivory  bobbins, 
wound  with  fine,  silk-covered  wire,  and  placed  on  opposite 
sides  of  a small  magnetic  needle  attached  to  the  pointer  of 
the  dial,  and  free  to  move  within  the  bobbins  to  the  right 
or  left  until  arrested  by  the  stops;  one  end  of  each  bobbin 
is  connected  to  the  line,  and  the  other  to  the  earth. 

The  signals  are  given  by  passing  a current  through  the 
coils  by  means  of  a battery  at  the  sending  station,  or  from 
a local  battery,  the  circuit  of  which  is  closed  by  a relay 
actuated  from  the  sending  station. 

The  wire  from  the  copper  pole  of  the  battery  is  attached 
to  the  binding  screw  C,  and  that  from  the  negative  or  zinc 
pole  to  the  binding  screw  Z;  the  binding  screws  A and  B 
are  connected  with  the  line  and  with  the  earth  respectively. 
The  axle  DF  of  the  commutator  is  made  in  two  parts — D and 
F,  of  gun-metal,  separated  by  some  insulating  substance, 
boxwood  being  the  one  most  generally  employed.  D is  con- 
nected by  a wire  to  C,  and  F to  Z. 

A steel  spring  p is  connected  by  means  of  a brass  bar  5, 
through  the  coils  and  the  receiver,  to  the  terminal  A;  and 
a second  steel  spring  p'  is  connected  by  means  of  the  brass 
bar  b'  with  the  terminal  B. 

When  the  needle  is  in  its  normal  or  vertical  position 
these  two  springs  rest  against  a projecting  pin  shown  in  the 
diagram,  and  thereby  maintain  the  continuity  of  the  line. 

From  the  upper  side  of  the  gun-metal  F,  and  from  the 
lower  side  of  the  gun-metal  D,  project  two  metallic  pins, 
7n,  ?7^'.  When  the  handle  is  in  its  normal  position  the 
pin  m remains  between  the  spring  p and  p'^  without  touch- 
ing either;  and  the  pin  m'  similarly  remains  between  the 
brass  bars  b and  5',  without  touching  them. 

When  the  handle  is  moved  to  the  left,  the  pin  m'  comes 


124 


ELECTRICITY  IN  MODERN  LIFE 


in  contact  with  the  brass  bar  6,  and  is  therefore  connected 
through  the  spring  p with  the  terminal  A,  connecting  the 
positive  pole  of  the  battery  to  the  line-wire;  at  the  same 
time  the  pin  m is  made  to  press  against  the  spring  and 
therefore  connects  it,  through  the  brass  bar  b\  with  the 
terminal  B,  connecting  the  negative  pole  of  the  battery  to 
the  earth;  and  a current  is  therefore  sent  round  the  line- 
wire  in  a certain  direction  and  deflects  the  needle.  If  the 
handle  is  turned  to  the  right,  m’  comes  in  contact  with 
and  connects  the  positive  pole  of  the  battery  to  earth,  while 

m is  pressed  against 
jp,  and  connects  the 
negative  pole  with 
the  line ; so  that  a 
current  will  be  sent 
round  the  line  in  the 
direction  opposite  of 
the  former  one,  and 
the  needle  will  be 
again  deflected.  If  the 
first  current  deflected 
it  to  the  right  it  will  now  turn  to  the  left,  and  vice  versd. 

In  the  needle-instrument  the  signals  are  discerned  by 
means  of  the  eye.  Audible  signals  are  now  very  largely 
used  in  place  of  visual  ones,  an  instrument  called  a sounder 
being  most  generally  used;  but  a pair  of  bells,  giving  two 
distinct  tones,  are  sometimes  employed. 

The  Sounder, — The  sounder  in  general  use  in  this  coun- 
try is  shown  in  Fig.  26.  E is  an  electro-magnet  formed 
of  an  upright  rod  of  soft  iron  surrounded  by  a coil  of  silk- 
covered  wire,  with  an  outer  covering  of  India-rubber,  or 
some  other  substance,  to  protect  it  from  injury.  The  ends 


OVERLAND  TELEGRAPHS 


125 


of  this  coil  are  connected  through  a pair  of  terminals 
attached  to  a wooden  base — one  only  of  which  is  shown 
in  the  diagram — to  the  line-wire  and  to  the  earth  respec- 
tively. The  armature  of  the  electro-magnet  consists  of  a 
bar  of  soft  iron  movable  about  a horizontal  axis  between 
two  stops,  a and  b. 

When  the  circuit  is  open  the  armature  is  pressed  up 
against  the  stops  by  means  of  the  spring  5,  the  tension  of 
which  may  be  varied  at  pleasure,  according  to  the  strength 
of  the  current  in  the  line-wire,  by  means  of  the  adjusting 
screw  shown  in  the  diagram.  When  the  circuit  is  closed, 
by  means  of  a key  at  the  transmitting  station,  a current  is 
sent  through  the  coil  of  the  electro-magnet,  which  magne- 
tizes it  as  long  as  the  current  is  passing,  and  therefore  pulls 
down  the  armature  against  the  stop  h.  The  sounds  are 
made  by  the  armature  striking  against  the  stops;  and  the 
letters  of  the  alphabet  are  denoted  by  various  combina- 
tions of  long  and  short  signals  respectively,  known  as  dots 
and  dashes,  separated  by  intervals  of  silence,  or  spaces. 
The  dots  are  formed  by  giving  a sharp  stroke  to  the  key; 
the  dashes,  by  depressing  it  more  slowly. 

It  is  evident  that  considerable  practice  would  be  required 
before  an  operator  would  be  able  to  transmit  or  to  read  off 
signals  of  this  kind  satisfactorily,  but  practiced  operators 
are  able  to  transmit  and  receive  messages  by  means  of  this 
instrument  with  extraordinary  rapidity. 

In  the  system  of  signals  employed,  a dash  is  considered 
to  be  equal  to  three  dots,  and  there  are  three  kinds  of  spaces 
employed — viz. , a space  equal  to  one  dot  between  the  differ- 
ent elements  of  a letter,  a space  equal  to  three  dots  between 
the  different  letters  of  a word,  and  a space  equal  to  six  dots 
between  two  words.  The  letters  E and  T,  being  those 


126 


ELECTRICITY  IN  MODERN  LIFE 


mostly  used,  are  represented  by  a single  dot,  and  a single 
dash  respectively,  and  the  other  letters,  numerals,  and  stops 
are  formed  of  combinations  of  these. 

The  key  employed  in  sending  the  message  is  shown  in 
its  simplest  form  in  Fig.  27.  It  consists  of  a brass  lever 
K in  permanent  connection  with  the  line-wire,  and  movable 
about  a horizontal  brass  axle  fixed  upon  an  insulating  sup- 
port of  wood  or  ebonite.  It  is  maintained  in  its  normal 
position,  viz.,  in  contact  with  the  stop  3,  by  means  of  a 


spring,  not  shown  in  the  figure,  and  thus  keeps  the  line- 
wire  in  connection  with  the  earth. 

When  the  key  is  depressed  2 is  brought  into  contact  with 
1,  and  the  current  from  the  battery,  shown  in  the  diagram 
by  the  ordinary  conventional  sign,  consisting  of  a series  of 
long  thin  lines  and  short  thick  ones  parallel  to  each  other, 
is  sent  through  the  line. 

It  is  evident  that  the  duration  of  the  current  will  depend 
upon  the  length  of  contact,  and,  to  use  an  illustration  due 


OVERLAND  TELEGRAPHS 


127 


to  Mr.  Preece,  dots  or  dashes  can  be  sent  by  striking  the 
key  exactly  as  one  would  the  keys  of  a piano  in  order  to 
produce  crotchets  or  quavers  respectively.  Another  form 
of  sounder,  which  is  extensively  used  in  America  on  rail- 
ways, and  in  other  places  where  external  noises  are  liable 


to  interfere  with  the  sound  of  the  instrument,  is  shown  in 
Fig.  28.  This  instrument  has  a very  heavy  armature  lever, 
and  the  downward  stroke  of  the  armature  takes  effect  upon 
an  arc  or  bridge,  as  shown  in  the  illustration,  thus  consider- 
ably increasing  the  volume  of  the  sound. 


128 


ELECTRICITY  IN  MODERN  LIFE 


When  the  line  is  of  any  great  length,  the  imperfect  insu- 
lation will  make  the  current  too  weak  to  work  a sounder 
without  the  use  of  a relay,  the  principle  of  which  was  de- 
scribed in  the  last  chapter. 

In  its  present  form  it  consists  simply  of  a more  delicate 
form  of  electro-magnet  than  the  one  employed  in  a sounder. 
It  is  wound  with  a very  large  number  of  turns  of  fine  wire, 
so  as  to  enable  the  weak  current  to  produce  as  great  a mag- 
netizing effect  as  possible  upon  the  core,  and  its  parts  are 
very  delicately  constructed,  so  that  a very  small  force  is 
sufficient  to  move  it.  In  the  simplest  forms  of  relay  the 
armature  is  of  soft  iron,  just  like  that  of  the  electro-magnet 


Fig.  29. 


of  the  Morse  sounder:  these  instruments  are  called  non- 
polarized relays  to  distinguish  them  from  polarized  relays, 
in  which  the  armatures  are  either  permanent  magnets,  or 
are  maintained  in  a magnetized  condition  by  means  of 
permanent-magnets  fixed  in  their  immediate  neighborhood. 
Polarized  relays  are  affected  by  the  direction  of  the  current, 
and  they  can  be  made  much  more  sensitive  than  the  non- 
polarized ones.  For  this  reason  the  latter  instruments  are 
very  seldom  used  in  this  country. 

The  Morse  Ink-  Writer, — This  is  an  instrument  of  an 
entirely  different  type  from  the  needle  telegraph  and  the 


OVERLAND  TELEGRAPHS 


129 


sounder,  in  that  it  gives  a permanent  record  of  the  messages 
sent.  A general  view  of  one  of  these  instruments  is  shown 
in  Fig.  29,  and  the  electrical  portion  of  the  apparatus  is 
shown  diagrammatically  in  Fig.  30. 

E is  an  electro-magnet,  of  the  same  character  as  that  em- 
ployed in  the  sounder,  and  is  worked  in  a similar  manner, 
by  means  of  a key  from  the  transmitting  station.  F is  a soft 
iron  armature  attached  to  the  lever /,  movable  about  a hori- 
zontal axis,  as  shown  in  the  diagram.  When  no  current 
is  passing  through  the  apparatus,  the  lever / is  kept  pressed 
against  the  stop  2,  by  means  of  the  spring  S,  the  tension  of 


Fig.  30. 


which  can  be  regulated  by  the  screw  C.  The  further  ex- 
tremity of  the  lever  carries  a small  disk  I,  movable  about 
a horizontal  axis,  and  dipping  into  a reservoir  of  ink.  The 
paper  is  carried  through  the  apparatus  by  means  of  an  ordi- 
nary clockwork  arrangement,  in  the  direction  shown  in  Fig. 
29,  and  this  clockwork  also  keeps  the  disk  I in  rotation, 
and  thus  insures  its  being  kept  wetted  with  ink. 

When  a current  is  sent  through  the  apparatus  from  the 
line,  the  armature  F is  attracted  toward  the  electro-magnet 
until  the  lever  / strikes  against  the  stop  3,  causing  the  disk 


130  ELECTRICITY  IN  MODERN  LIFE 

I to  come  in  contact  with  the  paper  and  record  a dot  or  a 
dash,  according  to  the  time  during  which  the  transmitting 
key  is  depressed.  The  play  of  the  lever  / can  be  adjusted 
by  means  of  the  screws  A and  B,  and  the  screw  G serves  to 
adjust  the  position  of  the  inking  disk  I,  while  the  attractive 
force  between  the  armature  and  the  electro-magnet  E can 

be  varied  by  raising  or 
lowering  the  coils  by 
means  of  the  screw  D. 

Wheatstone' s ABC 
Instrument — T his  in- 
strument is  a very  good 
type  of  a considerable 
number  of  telegraph  in- 
struments, in  which  the 
signals  are  recorded  by 
means  of  a pointer  mov- 
ing round  a dial  on 
which  the  letters  of  the 
alphabet  are  marked. 
Siemens,  Breguet,  and 
others  have  invented 
instruments  of  a similar 
character,  but  Wheat- 
stone’s is  the  form  usual- 
ly employed  in  England. 

An  ABC  telegraph  is  very  suitable  for  use  on  private 
wires,  where  great  rapidity  is  not  requisite,  as  it  can  be 
worked  by  any  person  of  ordinary  intelligence  without 
previous  practice.  Fig.  31  gives  a general  view  of  the 
instrument. 

When  the  handle  shown  in  front  is  rotated,  a soft  iron 


Science,  p.  \ix~VoL  13 


library 
OF  THE 

N'\'E?^G!TY  of  ILLINOIS 


OVERLAND  TELEGRAPHS 


131 


armature  is  made  to  spin  in  front  of  a pair  of  coils  surround- 
ing the  poles  of  a horseshoe  magnet,  thereby  generating  at 
each  revolution  four  currents  in  alternate  directions  through 
the  coils,  and  by  means  of  suitable  mechanism  each  current 
is  made  to  move  the  pointer  through  one  space.  In  order  to 
indicate  any  letter,  the  key  opposite  to  the  required  letter 
on  the  lower  dial  is  depressed,  and  the  handle  turned  until 
the  pointer  p comes  opposite  to  that  letter. 

When  this  takes  place  p is  prevented  from  turning  fur- 
ther, and  at  the  same  time  the  currents,  instead  of  going 
into  the  line-wire,  are  cut  off,  so  that  p,  and  the  pointer 
p'  on  the  indicating  dial  at  the  receiving  station,  remain 
pointing  to  the  same  letter. 

Hughes's  Type- Printing  Telegraph. — A good  many  instru- 
ments, some  of  exceeding  ingenuity,  have  been  devised,  in 
which  the  message  is  directly  printed  off  in  ordinary  type, 
just  as  if  it  had  been  done  by  means  of  one  of  the  type- 
writers now  in  general  use.  The  only  one  of  these  that 
has  been  employed  to  any  considerable  extent  in  Europe 
is  that  of  Hughes,  a general  view  of  which  is  shown  in 
Fig.  32.  The  instruments  at  the  transmitting  and  receiv- 
ing stations  are  exactly  similar,  and  are  made  to  move  in 
perfect  synchronism;  and  each  letter  is  registered  by  means 
of  a single  current  of  short  duration,  which  at  the  right 
moment  brings  a strip  of  paper,  carried  underneath  the 
type-wheel,  in  contact  with  the  wheel  ce,  at  the  edge  of 
which  are  placed  the  letters  of  the  alphabet,  so  that  the 
required  letter  is  printed  upon  the  strip  as  the  type-wheel 
is  made  to  revolve  by  means  of  suitable  mechanism.  The 
messages  are  sent  by  depressing  a series  of  keys  marked 
with  the  different  letters  and  numerals,  as  shown  in  the 
illustration. 


182 


ELECTRICITY  IN  MODERN  LIFE 


When  a key  is  depressed  it  raises  a pin,  and  this  pin 
catches  the  chariot  A,  which  rotates  the  type-wheel,  and 
sends  a current  to  the  distant  station,  causing  the  paper  at 
both  stations  to  be  pressed  up  against  the  type-wheel  at  the 
same  moment. 

The  Wheatstone  Automatic  Telegraph, — With  the  instru- 
ments previously  described  the  signals  have  to  be  trans- 
mitted directly  through  the  line  by  means  of  an  instrument 
worked  by  hand,  and  the  greatest  speed  attainable  does  not 
exceed  thirty  or  thirty-five  words  per  minute.  In  addition 
to  this,  an  operator  working  for  some  hours  at  his  maximum 


speed  will  naturally  become  tired,  and  therefore  not  only 
will  the  speed  at  which  he  can  work  be  gradually  reduced, 
but  errors  are  very  likely  to  be  made.  Now  Morse  signals 
can  be  sent  along  a line  and  recorded  by  an  ink-writer  at 
a very  much  greater  rate  than  any  clerk  can  send  by  hand ; 
hence  many  attempts  have  been  made  to  devise  some  means 
of  transmitting  messages  automatically,  and  the  system  most 
generally  employed  in  England  is  that  invented  by  Wheat- 
stone. 


THE  STORY  OF  THE  TELEGRAPH 


133 


Wheatstone’s  automatic  telegraph  consists  of  three  dis- 
tinct parts — viz.,  a perforator,  which  prepares  the  message 
by  punching  holes  in  a paper  ribbon ; a transmitter,  which 
sends  the  message  from  the  line  by  means  of  automatic 
machinery,  controlled  by  the  punched  paper  which  is  passed 
through  it;  and  a receiver,  which  records  the  message.  The 
general  appearance  of  the  perforator  is  shown  in  Fig.  33. 

It  will  be  seen  that  there  are  three  keys  in  the  front 
portion  of  the  apparatus,  and  each  time  that  one  of  these 
keys  is  struck  it  actuates  a mechanism  which  causes  a paper 
ribbon  to  move  forward  through  a definite  space,  and  at  the 
same  time  actuates  one  or  more  of  a series  of  five  punches, 
shown  at  1,  2,  3,  4,  6,  in  Fig.  34.  When  the  left-hand  key 


is  struck  it  causes  the  punches  1,  2,  and  3 to  perforate  the 
paper,  punching  out  three  clean  round  holes  in  a vertical 
line;  the  centre  key  actuates  the  punch  2 only,  making  a 
single  hole,  while  the  right-hand  key  depresses  the  four 
punches  1,  2,  4',  and  5.  The  punches  are  usually  struck 
with  small  wooden  mallets  held  in  the  hands.  The  series  of 
holes  made  by  the  left-hand  key  corresponds  to  a dot,  the 
single  hole  made  by  the  centre  key  to  a space,  and  the  set 
of  four  holes  made  by  the  right-hand  key  to  a dash.  The 
holes  made  by  the  centre  key  are  in  the  centre  of  the  ribbon, 
as  shown  in  Fig.  34,  and  they  are  smaller  than  the  upper 
and  lower  holes. 

A small  toothed  star-wheel,  which  turns  through  a defi- 


134 


ELECTRICITY  IN  MODERN  LIFE 


nite  space  when  a key  is  depressed,  fits  into  these  holes, 
and  moves  the  paper  a step  onward  at  each  depression. 
It  will  be  seen  that  for  each  dash  two  central  holes  are 
punched,  so  that  the  paper  will  move  twice  as  far  for  a dash 
as  for  a dot.  Fig.  35  shows  a strip  of  paper  thus  prepared 
to  indicate  the  word  “Paris,”  by  means  of  dots  and  dashes, 
as  shown  on  the  lower  part  of  the  strip  in  the  diagram. 

The  transmitter  is  a very  complicated  piece  of  apparatus, 
which  is  made  to  send  a series  of  currents  in  opposite  direc- 
tions into  the  line  under  the  control  of  the  punched  paper. 
The  strip  of  paper  is  carried  through  the  instrument  by 
means  of  the  star-wheel  working  into  the  central  row  of 


FiCx.  35. 


holes,  and  two  vertical  rods  are  pressed  upward  against  the 
ribbon  by  means  of  springs,  and  are  placed  in  such  positions 
that  they  will  enter  the  two  outside  series  of  holes  as  they 
pass  above  them.  The  rods  work  a disk  which  acts  as  a com- 
mutator, each  entry  of  the  rod  into  a hole  on  one  side  of  the 
ribbon  sending  a current  through  the  line  in  one  direction, 
and  each  entry  of  the  rod  into  a hole  on  the  other  side  of 
the  ribbon  sending  a current  in  the  reverse  direction.  The 
punching  which  corresponds  to  a dash  reverses  the  current 
after  an  interval  twice  as  long  as  when  the  holes  punched 
correspond  to  a dot.  If  there  were  no  paper  in  the  instru- 
ment the  rods  would  move  up  and  down  alternately. 


THE  STORY  OF  THE  TELEGRAPH 


135 


When  one  of  the  rods  has  entered  a hole,  as  the  in- 
strument continues  to  move  it  is  drawn  out,  and  the  paper 
moved  on  either  through  one  or  two  spaces,  according  to 
whether  a dot  or  a dash  is  to  be  sent  when  the  other  rod 
next  enters  a hole. 

This  transmitter  will  work  at  a speed  of  450  words  a 
minute  on  a short  line,  but  more  slowly  over  a long  line, 
owing  to  the  wire  becoming  charged  very  much  like  a Ley- 
den jar.  The  amount  of  this  electro-static  charge  depends 
on  the  length  and  surface  of  the  wire  and  its  distance  from 
the  earth,  as  well  as  on  the  nature  of  the  insulating  material, 
whether  simply  air,  or  partly  India-rubber  or  gutta-percha, 
which  separates  it  from  the  earth.  The  result  of  a portion 
of  the  current  being  absorbed  in  producing  this  electro- 
static charge  is  that  a momentary  current,  such  as  would 
be  produced  by  simply  touching  the  key  and  raising  the 
finger  immediately,  would  produce  little  or  no  effect  at 
the  further  end  of  a long  telegraph  line,  and  therefore 
the  instrument  has  to  be  worked  more  slowly  as  the  line 
increases  in  length. 

The  receiver  employed  with  the  automatic  transmitter  is 
simply  a Morse  ink-writer  of  a more  delicate  and  sensitive 
character  than  the  one  already  described.  With  a Wheat- 
stone automatic  instrument  a number  of  clerks  can  be  em- 
ployed to  punch  strips  corresponding  to  the  messages,  and 
these  can  be  run  rapidly  one  after  the  other  through  the 
transmitter,  thus  greatly  reducing  the  number  of  lines 
necessary  between  two  places  where  the  traffic  is  heavy. 

Another  way  in  which  the  capacity  of  a line  can  be 
increased  consists  in  employing  an  arrangement  by  means 
of  which  two  or  more  sets  of  messages  can  be  sent  simulta- 
neously in  opposite  directions  along  the  same  wire  without 


136 


ELECTRICITY  IN  MODERN  LIFE 


interfering  with  each  other.  The  arrangement  adopted  for 
sending  two  messages  simultaneously  is  called  duplexing 
the  line,  and  it  will  be  of  interest  to  describe  briefly  one 
among  the  various  methods  by  which  this  is  effected. 

Duplex  Telegraphy, — Let  two  stations,  A and  B,  be  con- 
nected together,  as  shown  in  Fig.  36,  in  which  P,  P'  rep- 
resent receiving  instruments,  or  relays  working  receiving 
instruments,  and  K,  K'  are  the  transmitting  keys  at  the  two 
stations.  It  will  be  seen  that  the  line  is  carried  from  the 
earth,  E,  through  an  adjustable  resistance,  R,  along  the  path, 
c,  a,  (7,  C,  &,  c',  to  a second  adjustable  resistance,  R',  con- 
nected with  the  earth  at  E'.  The  resistances  R and  R'  are 


Fig.  36. 


made  equal  to  that  of  the  line  at  the  time  of  working, 
a G and  a c are  two  fixed  resistances  equal  to  each  other, 
as  also  are  h G'  and  h c'. 

The  line  is  earth  connected  at  a and  b,  by  means  of  the 
keys  K and  K',  either  directly,  or  through  the  correspond- 
ing battery,  according  as  the  key  is  in  its  normal  position, 
or  is  depressed.  When  the  key  K is  depressed,  a current 
is  sent  from  the  battery  through  the  point  a where  the  line 
divides,  part  going  along  the  line  a G G'  b c\  and  to  earth 
at  E',  while  the  other  part  goes  to  earth  at  E by  the  path 
a c E.  Since  the  resistance  of  a C is  equal  to  that  of  a c, 
the  electro-motive  force  produced  at  a,  by  means  of  the 


THE  STORY  OF  THE  TELEGRAPH 


137 


battery,  will  produce  the  same  potential  at  the  points  G and 
c,  and  therefore  no  current  will  flow  along  the  path  (7  P c, 
so  that  the  instruments  at  P will  not  be  affected  by  any 
motions  of  the  key  K,  which,  however,  will  affect  the  instru- 
ments at  P'.  In  the  same  way  the  current  sent  from  B,  by 
means  of  the  key  K',  will  affect  the  instruments  at  P,  but 
will  have  no  effect  upon  those  at  P'. 

Not  very  long  after  Duplex  Telegraphy  was  first  intro- 
duced by  Gintl,  of  Vienna,  it  was  extended  by  Edison  so 
as  to  enable  two  sets  of  signals  to  be  sent  simultaneously 
in  opposite  directions,  forming  what  is  known  as  “Quadru- 
plex  Telegraphy.” 

This  was  still  further  developed  by  Delany  into  the  sys- 
tem of  “Multiplex  Telegraphy,”  by  which  three  or  more 
sets  of  messages  can  be  sent  at  the  same  time  in  opposite 
directions  along  a single  wire. 

The  Writing  Telegraph. — I must  not  conclude  the  descrip- 
tion of  modern  telegraphic  apparatus  without  mentioning  a 
very  interesting  telegraphic  instrument  of  recent  invention — 
viz.,  the  Writing  Telegraph  of  Mr.  J.  H.  Robertson.  By 
means  of  this  instrument  a message  written  by  an  operator 
at  the  sending  station  on  a slip  of  paper,  carried  along  at  a 
uniform  rate  by  means  of  clockwork,  is  reproduced  in  fac- 
simile at  the  receiving  station.  This  was  not  the  first  writ- 
ing telegraph,  as  one  of  a somewhat  similar  character  was 
invented  by  Mr.  E.  A.  Cowper;  but  Cowper’s  was  not  a 
form  suitable  for  practical  use.  Robertson’s  instrument, 
on  the  contrary,  can  be,  and  is  actually,  employed  for  prac- 
tical purposes  in  America,  though  hitherto  the  post-office 
monopoly  has  prevented  its  use  in  this  country.  It  requires 
two  circuits  for  each  pair  of  instruments,  or  the  equivalent 
of  two  circuits — viz.,  a single  circuit  duplexed. 


188 


ELECTRICITY  IN  MODERN  LIFE 


The  transmitter  of  the  writing  telegraph,  shown  in  Fig. 
37,  consists  of  two  piles  of  disks  of  exceedingly  fine  com- 
pressed carbon,  placed  with  their  axes  at  right  angles,  and 
each  pile  is  provided  with  a screw  for  regulating  the  press- 
ure between  the  disks.  The  two  piles  form  portions  of  the 
two  circuits  required  to  connect  the  transmitting  with  the 
receiving  station,  one  pile  being  contained  in  each  circuit. 

The  transmitting  pen  consists  of  a rod,  shown  in  the 
diagram,  which  is  pivoted  at  its  lower  end  between  the  two 
piles,  and  is  provided  with  pressure 
points,  which  exert  a varying  pressure 
upon  one  end  of  each  pile  of  disks 
when  the  rod  is  moved  about  in  any 
manner.  The  motions  of  this  rod  are 
effected  by  means  of  the  stylus  pivoted 
to  its  upper  extremity. 

When  the  instrument  is  put  to- 
gether ready  for  use,  the  rod  passes 
through  a small  square  hole  in  the 
top  of  the  case,  and  the  operator  writes 
by  moving  this  stylus  just  as  he  would 
a pen. 

As  the  pressure  points  of  the  trans- 
mitting-rod  press  more  strongly  against 
either  pile  of  carbon  disks,  the  contact 
between  the  separate  disks  in  that  pile 
is  improved,  and  therefore  the  electri-  fig.  37. 

cal  resistance  of  the  corresponding  circuit  is  diminished, 
and  the  current  in  it  therefore  increased. 

The  receiving  apparatus  consists  of  a pair  of  electro- 
magnets arranged  at  right  angles  to  each  other,  as  shown 
in  Fig.  38.  The  armatures  of  these  magnets  are  attached  to 


. 13 


THE  STORY  OF  THE  TELEGRAPH 


139  ^ 


a rod,  pivoted  at  its  lower  extremity  between  the  adjacent 
poles  of  the  electro-magnets,  as  shown  in  the  diagram.  The 
pen  of  the  receiver  is  similar  in  principle  to  the  well-known 
stylographic  pen,  and  is  attached,  as  shown,  to  the  upper 
extremity  of  the  armature  rod.  The  coils  of  one  of  the 
electro-magnets  of  the  receiver  form  a portion  of  the  circuit 
containing  one  of  the  sets  of  carbon  disks,  while  the  coils  of 
the  second  electro-magnet  are  included  in  the  circuit  con- 
taining the  other  pile  of  disks.  As  the  transmitting  stylus 
is  moved,  the  resulting  continuous  variation  in  the  strength 
of  the  currents  in  the  two 
circuits  causes  a correspond- 
ing continuous  variation  in 
the  attraction  exerted  by 
the  two  electro-magnets  re- 
spectively upon  their  com- 
mon armature,  and  in  this 
manner  the  rod  carrying 
the  pen  is  made  to  move 
in  a path  exactly  similar  to 
that  of  the  transmitting  rod. 

In  the  original  form  of 
the  instrument  the  pen  by 
which  the  message  was 
written  at  the  transmitting 
station  was  rigidly  attached  to  the  transmitting  stylus, 
but  this  pen  was  afterward  done  away  with. 

As  the  operator  at  the  transmitting  station  moves  his 
stylus,  his  own  pen,  in  circuit  with  the  line,  travels  over 
the  paper  ribbon  of  his  own  instrument,  moved  forward  at 
a uniform  rate  by  clockwork,  in  obedience  to  the  motions 
of  the  stylus,  thus  enabling  him  to  see  what  he  is  writing. 


Fig.  38. 


140 


ELECTRICITY  IN  MODERN  LIFE 


and  to  be  certain  that  the  motions  of  his  stylus  are  such  as 
to  produce  a legible  message.  Since  the  pens  at  the  two 
stations  move  in  synchronism  under  the  influence  of  the 
same  pair  of  circuits,  any  variation  in  the  current,  due  to 
variation  in  the  resistance  of  the  line,  or  to  changes  in  its 
insulation,  produces  a similar  efiect  on  the  motion  of  each 
pen,  so  that  the  two  pens  move  in  such  exact  harmony  with 
each  other  that  it  is  quite  impossible,  by  the  closest  com- 
parison, to  distinguish  one  of  the  written  ribbons  from 
the  other.  It  is  difficult  at  first  to  produce  legible  writ- 
ing with  this  instrument,  owing  to  the  novelty  of  writing 
with  the  pen  moving  always  within  the  same  small  area 
while  the  paper  travels  on  beneath  it. 

A letter  with  a backward  turn,  such  as  a G or  an  S,  has 
to  be  made  pretty  sharply,  or  the  paper  will  have  travelled 
on  too  far  to  allow  of  the  letter  being  legibly  made. 

This  difficulty  was  advanced  as  an  objection  against  the 
practical  use  of  the  instrument,  by  many  who  were  other- 
wise very  much  taken  with  its  beauty  and  simplicity,  when 
it  was  first  exhibited,  three  years  ago,  at  the  American 
Exhibition  in  London.  The  difficulty,  however,  is  more 
imaginary  than  real,  for,  in  experimenting  with  the  instru- 
ment myself,  I found  that  after  about  twenty  minutes’  prac- 
tice I was  able,  without  any  difficulty,  to  write  a perfectly 
legible  message.  The  instrument  is  one  which  would  almost 
certainly  have  been  very  extensively  used  if  it  had  been 
introduced  before  the  telephone  was  known. 

Telegraph  Lines, — Telegraph  lines  in  country  districts  are 
generally  supported  upon  poles  fixed  in  the  ground,  and  in 
this  country  wooden  posts  are  almost  invariably  used  for 
this  purpose,  the  timber  employed  being  principally  Swedish 
or  Norwegian  pine.  In  order  to  preserve  the  poles  from 


THE  STORY  OF  THE  TELEGRAPH 


141 


decay,  they  are  first  well  seasoned  by  exposure  for  a con- 
siderable time  to  free  currents  of  air,  in  order  to  dry  up  all 
the  sap,  after  which  the  portion  of  the  pole  which  is  to  be 
imbedded  in  the  ground  is  slightly  charred,  and,  before 
being  placed  in  position,  the  bottom  of  the  pole  is  thor- 
oughly coated  with  tar,  so  as  to  prevent  the  absorption  of 
moisture.  Poles  of  this  kind  will  generally  last  for  about 
seven  years  without  renewal,  but  they  may  be  made  to  last 
a very  much  longer  time  by  saturating  them  with  creosote, 
one  of  the  products  obtained  by  the  distillation  of  coal-tar. 
The  poles  are  creosoted  by  being  placed  in  air-tight  cylin- 
ders, from  which  the  air  is  carefully  exhausted,  after  which 
creosote  is  forced  in  under  pressure,  which  is  kept  up  until 
a sufficient  amount  has  been  absorbed. 

The  holes  in  which  the  poles  are  planted  used  formerly 
to  be  dug  by  means  of  the  spade  and  pick,  but  these  imple- 
ments have  now  been  replaced,  to  a very  great  extent,  by 
the  earth-borer,  which  is  something  like  a large  auger,  and 
does  the  work  much  more  rapidly,  and  therefore  more 
economically,  than  the  pick  and  shovel.  When  the  pole 
has  been  placed  in  position,  the  earth  must  be  very  firmly 
rammed  in  all  round  it,  or  'punned^  as  it  is  called,  in  order 
to  prevent  the  pole  from  gradually  falling  over  to  one 
side. 

When  the  poles  are  of  moderate  length,  and  only  have  to 
support  a small  number  of  wires,  this  is  generally  sufficient; 
but  when  very  high  poles  are  employed,  or  if  they  have  to 
carry  a large  number  of  wires,  they  are  frequently  strength- 
ened, either  by  means  of  stays  of  iron  wire,  the  upper  ends 
of  which  are  attached  to  the  poles  near  the  top,  and  the 
lower  ends  to  weights  buried  in  the  ground  at  a little  dis- 
tance from  the  base,  or  by  means  of  rigid  wooden  or  iron 


142 


ELECTRICITY  IN  MODERN  LIFE 


struts,  the  lower  portions  of  which  are  buried  in  the  ground 
at  some  distance  from  the  base,  while  the  upper  ends  are 
attached  to  the  poles. 

In  this  country  the  wires  are  generally  insulated  by  being 
fixed  to  porcelain  cups  attached  to  the  poles.  The  cups  are 
made  of  such  a form  as  to  expose  the  upper  portions  freely 
to  the  cleansing  action  of  the  rain,  while  the  lower  portions 
are  shielded  from  the  rain  so  as  to  keep  them  fairly  dry, 
and  preserve  the  insulation  as  much  as  possible  during 
wet  weather.  The  wires  are  attached  to  the  insulators  by 
being  wound  round  them  and  firmly  soldered  together, 
so  that  if  a breakage  takes  place  at  any  point,  the  wire 
between  the  neighboring  poles  will  not  be  dragged  from  its 
supports,  but  the  broken  ends  will  simply  fall  where  the 
breakage  takes  place. 

In  places  where  there  is  danger  of  trees  falling  on 
the  wires,  as,  for  example,  in  some  parts  of  America,  insu- 
lators consisting  of  glass  blocks  with  slits  cut  in  them  are 
largely  employed,  the  wire  being  simply  passed  through 
the  slits,  leaving  a good  deal  of  slack;  and  if  a tree  then 
falls  across  the  line,  it  usually  bears  the  wire  down  with  it, 
taking  up  the  slack  from  the  neighboring  poles,  but  not 
breaking  it,  and  it  will  therefore  generally  stick  in  the 
branches  without  being  brought  down  to  the  ground,  so  that 
the  circuit  will  not  be  entirely  interrupted. 

When  telegraph  wires  have  to  be  taken  through  towns 
they  are  usually,  when  only  few  in  number,  carried  over 
the  tops  of  the  houses,  to  which  they  are  attached  by  means 
of  porcelain  insulators  fixed  to  iron  supports.  If,  however, 
the  wires  are  numerous,  they  are  generally  carried  under- 
ground, a number  of  wires  being  drawn  together  into  iron 
or  earthenware  pipes,  provided  with  what  are  called  flush 


THE  STORY  OF  THE  TELEGRAPH 


143 


boxes,  at  intervals  of  every  one  hundred  yards  when  the 
line  is  fairly  straight,  or  at  more  frequent  intervals  if 
it  winds  to  any  considerable  extent.  These  flush  boxes 
are  provided  with  closely -fitting  covers,  to  prevent,  as  far 
as  possible,  the  entrance  of  moisture.  The  post-office  tele- 
graph wires  in  London  are  almost  invariably  laid  in  this 
manner,  the  pipes  employed  being  of  cast-iron,  usually  four 
inches  in  diameter,  except  where  only  a few  wires  are  likely 
to  be  required,  when  smaller  pipes  are  used.  A four-inch 
pipe  will  take  as  many  as  one  hundred  and  twenty-eight 
wires  of  the  kind  employed  in  the  post-office  telegraph 
system.  Each  wire  has,  of  course,  to  be  insulated  by  means 
of  a covering,  which  is  usually  of  gutta-percha  or  India- 
rubber.  Overland  telegraph  wires  in  tropical  countries, 
such,  for  example,  as  Australia  and  India,  are  usually 
carried  upon  iron  posts,  as  the  wooden  ones  would  soon  be 
destroyed  by  the  attacks  of  the  white  ants  or  other  insects, 
unless  protected  by  creosote  or  some  similar  preservative 
process,  which,  however,  in  this  case,  would  involve  much 
heavier  expense  than  the  employment  of  iron  posts. 

The  use  of  iron  posts  in  countries  where  transport  is  diffi- 
cult has  the  additional  advantage  that  they  are  very  much 
lighter  than  wooden  ones,  and  also  that  they  can  be  made 
in  sections  and  put  together  at  the  place  where  they  are 
to  be  erected. 

A very  convenient  form  of  iron  post,  extensively  em- 
ployed in  Australia,  was  designed  by  Oppenheimer  of  Man- 
chester. Its  base  consists  of  a sort  of  inverted  pyramid  with 
moderately  sharp  cutting  edges,  and  it  is  driven  into  the 
ground  by  the  blows  of  a descending  weight  which  slides 
on  the  pole,  and  by  means  of  a tripod  arrangement  is  drawn 

up  to  a moderate  height  and  then  allowed  to  fall  upon  the 

Science— VoL.  XITI— 7 


144 


ELECTRICITY  IN  MODERN  LIFE 


base  until  the  upper  or  flat  portion  of  the  base  is  level  with 
the  ground. 

In  selecting  the  wire  for  a telegraph  line,  the  chief  con- 
siderations by  which  the  choice  must  be  determined  are — 
low  electrical  resistance  and  durability,  and  also,  when  the 
wires  are  suspended  on  poles,  mechanical  strength. 

The  first  two  conditions  are  best  fulfilled  by  copper,  but 
until  recently  it  has  been  difficult  to  get  copper  wire  with 
much  mechanical  strength,  except  at  a very  high  cost,  and 
for  this  reason  iron  wires  are  almost  universally  employed 
upon  lines  carried  on  poles,  copper  being  used  for  under- 
ground lines.  Copper  wire  is  now,  however,  being  produced 
which  has  a tensile  strength  almost  equal  to  that  of  steel, 
and  a very  low  electrical  resistance,  and  that  at  a cost  con- 
siderably less  than  used  formerly  to  be  paid  for  ordinary 
commercial  copper  wire.  It  is  therefore  very  possible  that 
copper  wires  may  come  into  general  use  in  the  near  future, 
for,  in  addition  to  the  electrical  resistance  of  copper  being 
much  lower  than  that  of  iron,  it  will  stand  exposure  to  the 
weather  for  a very  much  longer  time. 

Faults, — Preece  and  Sivewright,  in  their  work  on  the 
telegraph,  from  which,  by  the  kind  permission  of  the  au- 
thors and  publishers,  most  of  the  illustrations  of  the  present 
chapter  have  been  taken,  classify  faults  occurring  upon 
telegraph  lines  under  three  heads — viz.,  disconnections, 
earths,  and  contacts;  which  they  then  subdivide  into  total, 
partial,  and  intermittent.  A total  disconnection  may  be 
caused  by  a tree  falling  across  the  wire  and  breaking  it,  or 
by  the  wire  being  broken  by  the  weight  of  the  snow  which 
accumulates  upon  it  in  a snowstorm;  while  partial  discon- 
nection may  be  produced  by  means  of  badly-made  joints 
or  bad  earth  connections,  or  by  some  of  the  joints  of  the 


THE  STORY  OF  THE  TELEGRAPH 


145 


instruments  not  being  kept  properly  clean.  Total  discon- 
nection is  of  course  indicated  by  the  absence  of  current 
in  the  line  when  the  battery  is  put  on,  and  a partial  dis- 
connection is  shown  by  the  strength  of  the  current  falling 
below  its  proper  value.  Earths  are  indicated  by  an  increase 
in  the  strength  of  a current  at  the  transmitting  station,  and 
its  decrease  or  entire  cessation  at  the  other  end.  A com- 
plete, or,  as  it  is  called,  a dead  earth,  is  caused  by  a wire 
resting  on  damp  earth,  or  coming  into  contact  with  a wire  or 
other  object  connected  with  the  earth.  Partial  earths  are 
caused  by  defects  in  the  insulators,  or  by  the  wire  coming 
into  contact  with  imperfect  conductors,  such  as  walls,  posts, 
or  trees,  in  connection  with  the  earth. 

Contacts  are  caused  by  one  wire  touching  another,  or  by 
two  wires  being  partially  connected,  either  by  means  of  an 
imperfect  conductor  falling  across  the  wires,  or  by  defects 
in  the  insulators  allowing  the  current  in  one  wire  to  leak 
into  another.  When  a number  of  wires  are  carried  on  the 
same  poles,  a great  deal  of  trouble  would  be  caused  by  this 
cross  leakage  if  special  precautions  were  not  taken  to  pre- 
vent it,  and  this  would  be  especially  noticeable  in  wet 
weather,  when  the  deposition  of  moisture  on  the  insulators 
greatly  diminishes  their  insulating  power.  The  effect  of 
this  cross  leakage  would  be  that  the  messages  sent  along 
one  wire  would  be  transmitted  to  stations  on  other  lines, 
and  interfere  with  the  messages  travelling  along  them. 

In  order  to  obviate  this  inconvenience,  the  base  of  each 
of  the  insulators  is  connected,  by  means  of  a short  wire,  to 
an  earth  wire  carried  down  the  pole  into  the  ground;  and 
as  this  path  offers  a much  smaller  resistance  than  that  from 
one  wire  to  another,  whatever  leakage  occurs  will  all  go 
to  earth,  and  the  effect  of  this  leakage  can  be  remedied 


146 


ELECTRICITY  IN  MODERN  LIFE 


by  increasing  the  battery  power  at  the  sending  station. 
These  earth  wires  also  act  as  lightning  conductors,  and  it 
is  a matter  of  great  importance  that  efficient  means  should 
be  provided  for  the  lightning  to  escape  to  earth  when  it 
strikes  a post,  instead  of  travelling  along  the  wires,  when 
it  would  destroy  the  instruments,  and  possibly  some  of  the 
operators  as  well. 

In  addition  to  these  earth  wires  attached  to  the  poles,  the 
instruments  themselves  are  protected  by  means  of  special 
lightning  protectors. 

The  lightning  protectors  employed  on  the  post-office 
lines,  and  which  are  found  to  be  extremely  efficient,  con- 
sist of  two  flat  brass  plates,  with  their  opposite  surfaces 
carefully  tinned  to  prevent  oxidation,  and  kept  at  a small 
distance  apart  by  means  of  thin  paraffined  paper  or  mica. 

One  of  these  plates  is  connected  to  the  line  and  the  other 
to  the  earth,  and  it  is  found  that  when  a lightning  discharge 
strikes  the  wire,  it  will  jump  across  the  small  distance 
and  go  to  earth,  in  preference  to  going  round  the  circuit. 
Intermittent  faults  are  often  caused  by  the  action  of  the 
wind  blowing  the  lines  against  different  bodies,  or  by  bodies 
being  brought  into  contact  with  them  at  intervals,  owing  to 
expansion  and  contraction  by  heat. 

In  order  to  enable  faults  to  be  localized  and  remedied 
with  despatch,  the  wires  on  overhead  lines  are  carried  at 
intervals  into  testing  boxes,  and  if  a fault  is  found,  tests 
are  applied  at  these  in  succession  until  the  fault  is  shown 
to  occur  between  two  adjacent  ones.  In  the  underground 
lines  the  flush  boxes  serve  the  same  purpose.  When  the 
fault  is  thus  localized  the  section  in  which  it  occurs  is  cut 
out,  the  exact  position  of  the  fault  ascertained,  and  the  wire 
repaired.  If  the  section  forms  part  of  a busy  circuit,  from 


THE  STORY  OF  THE  TELEGRAPH 


147 


which  a wire  cannot  easily  be  spared,  a section  is  usually 
cut  out  from  a less  busy  circuit  and  introduced  into  the 
former  one  until  the  repair  has  been  effected. 

In  a properly  organized  system  no  serious  interruption 
will  take  place,  unless  in  consequence  of  an  extensive  series 
of  breakdowns,  such  as  sometimes  occurs  during  an  excep- 
tionally heavy  snowstorm,  for  the  borrowed  wire  will  always 
be  taken  from  a circuit  which,  in  addition  to  not  having 
any  very  heavy  traffic  at  the  time,  also  possesses  an  alterna- 
tive route. 

The  overland  telegraph  system,  like  most  other  impor- 
tant undertakings  in  this  country,  was  inaugurated  and 
developed  by  private  enterprise,  but  in  the  year  1870  it  was 
purchased  by  the  Grovernrnent  and  placed  under  the  direct 
control  of  the  Postmaster-General.  One  of  the  most  cher- 
ished privileges  of  an  Englishman  is  his  right  of  grumbling 
at  the  Government  and  every  undertaking  under  its  direc- 
tion; and  in  many  cases  there  is  very  good  reason  for  such 
grumbling,  for  the  waste  in  many  Government  departments 
is  simply  scandalous;  and  red  tape,  moreover,  has  been  one 
of  the  most  formidable  obstacles  to  the  successful  develop- 
ment of  many  a valuable  scientific  invention.  If,  however, 
the  post-office  telegraph  system  is  to  be  judged  by  its  re- 
sults, as  seems  only  fair,  there  will  not^  I think,  be  found 
much  scope  for  legitimate  fault-finding.  In  the  year  1870, 
when  it  was  bought  by  the  Government  at  twenty  years’ 
purchase,  the  telegraph  system  was  bringing  in  an  income 
of  about  £550,000  a year,  and  this  has  now  increased  to  over 
£2,000,000  annually,  the  number  of  messages  transmitted 
having  increased  in  the  same  time  from  6,000,000  to 
53,400,000. 

Mr.  Preece,  from  whose  most  interesting  address  to  the 


148 


ELECTRICITY  IN  MODERN  LIFE 


British  Association  at  Bath  these  figures  are  taken,  reminds 
us  in  another  portion  of  his  address  how  easily  accidental 
errors  may  creep  into  telegraph  messages  without  any  fault 
on  the  part  of  the  operator.  He  tells  us,  for  example,  that 
a lightning  flash  in  America  might  cause  an  extra  dot  in 
Europe,  causing  mine  to  become  wine;  or  an  earthquake 
in  Japan  might  cause  the  addition  of  a dash  and  turn  life 
into  wife  ; or  again,  a wild  goose  flyibg  against  a telegraph 
wire  might  drive  it  into  contact  with  another  wire  and  turn 
sight  into  night.  And  yet  he  says,  as  a matter  of  fact,  in 
ninety-nine  cases  out  of  a hundred  the  telegraph  operator 
delivers  to  the  editor  of  a newspaper  copy  which  is  far 
more  accurate  than  the  first  proofs  submitted  by  the  printer 
of  his  own  leader.  As  an  example  of  the  enormous  strain 
which  is  sometimes  thrown  upon  and  successfully  borne 
by  the  post-office  officials,  Mr.  Preece  tells  us  that  on  the 
occasion  of  the  introduction  of  Mr.  Gladstone’s  Home  Rule 
Bill,  on  the  8th  of  April,  1886,  no  less  than  1,500,000  words 
were  sent  from  the  Central  Telegraph  Office  in  London. 

If  it  were  not  for  the  telegraph  it  would  be  quite  impos- 
sible to  carry  on  the  railway  traffic  of  the  country  with  its 
present  combined  celerity  and  safety.  Most  railways  are 
now  worked  on  the  block  system,  according  to  which 
the  line  is  broken  up  into  short  sections,  and  only  one 
train  is  allowed  on  any  section  at  the  same  time,  the  moment 
at  which  it  enters  upon  any  given  section  being  signalled 
from  one  signal-box  to  the  other,  and  no  other  train  is 
allowed  to  enter  until  the  signalman  has  telegraphed  that 
the  section  is  clear.  At  the  more  important  junctions  the 
system , of  ^electrical  signals  is  supplemented  by  ingenious 
mechanical  arrangements  which  make  it  impossible  for 
the  signalmen,  through  inadvertence,  to  make  any  com- 


THE  STORY  OF  THE  TELEGRAPH 


149 


bination  of  signals  which  would  lead  to  an  accident;  and, 
as  Mr.  Preece  tells  us  in  his  address,  ‘‘the  signalman  is  able 
to  survey  the  line  all  round  and  about  him.  By  aid  of  his 
electrical  signals  he  can  talk  by  telephone  or  telegraph  to 
his  neighbors,  or  his  station-master;  he  learns  of  the  motion 
of  the  trains  he  is  marshalling  by  the  different  sounds  of 
electric  bells;  he  controls  his  outdoor  signals  by  the  deflec- 
tion of  needles,  or  the  movements  of  miniature  semaphores; 
he  learns  the  true  working  of  his  distant  signals  by  their 
electrical  repetition.  Machinery  governs  and  locks  every 
motion  he  makes,  so  that  he  cannot  make  a mistake.” 

The  increase  in  the  safety  of  railway  travelling  is  shown 
by  the  figures  given  on  the  same  occasion  by  Mr.  Preece, 
according  to  which,  while  in  the  five  years  ending  with  1878 
thirty -five  people  on  the  average  were  killed  annually  from 
causes  beyond  their  own  control — in  the  five  years  ending 
with  1887  the  average  had  been  reduced  to  sixteen,  which 
means  that  only  one  person  is  killed  in  36,000,000  railway 
journeys. 


150 


ELECTRIQITY  IN  MODERN  LIFE 


CHAPTER  XI 

SUBMARINE  TELEGRAPHS 

The  first  attempts,  as  far  as  is  known,  at  sending  the 
electric  current  through  submerged  conductors  were 
made  by  Sommering,  who  about  the  year  1808  made 
some  experiments  of  the  kind  in  St.  Petersburg  for  the  pur- 
pose of  exploding  gunpowder  at  a distance;  and  in  1815  he 
repeated  his  experiments  in  Paris,  by  means  of  a conductor 
laid  upon  the  bottom  of  the  Seine. 

After  the  invention  of  his  electro-chemical  telegraph, 
described  in  Chapter  IX.,  Sommering  proposed  that  Cron- 
stadt  and  St.  Petersburg  should  be  joined  by  means  of 
a submarine  telegraph  line,  but  the  project'  was  never 
carried  out. 

Ronalds  also  pointed  out  the  possibility  of  submarine 
telegraph  cables  a few  years  later;  but  the  first  experiments 
in  which  telegraphic  signals  were  actually  transmitted  under 
water  appear  to  have  been  made  in  1839  by  an  Irishman, 
Dr.  O’Shaughnessy,  who  employed  conductors  made  of  wire, 
covered  over  with  pitch  and  tarred  hemp,  and  succeeded 
without  any  difficulty  in  transmitting  signals. 

In  1887  Wheatstone  proposed  laying  a cable  from  Dover 
to  Calais,  to  be  worked  by  the  needle  apparatus  invented 
by  Cooke  and  himself,  and  described  in  Chapter  X.,  and 
in  the  following  year  a committee  of  the  House  of  Commons 


SUBMARINE  TELEGRAPH 


151 


was-  appointed  to  inquire  into  the  subject.  Some  pre- 
liminary experiments,  however,  which  were  made  at  the 
Observatory  of  Brussels  were  not  altogether  satisfactory, 
and  the  project  was  dropped. 

Wheatstone  made  some  further  experiments  in  Swansea 
Bay  in  1844,  and  in  the  following  year,  when  gutta-percha 
was  first  introduced  into  this  country,  he  at  once  perceived 
its  value  as  an  insulator  for  submarine  telegraph  wires. 

Morse  also  turned  his  attention  to  the  subject,  and  made 
some  experiments  with  an  insulated  submerged  wire  at  New 
York  in  1842,  and  in  the  following  year  he  submitted  to  the 
American  Grovernment  a project  for  establishing  telegraphic 
communication  between  America  and  Europe. 

In  1845  Cornell  laid  down  a cable  twelve  miles  long  in 
the  Hudson  River  to  establish  communication  between  Fort 
Lee  and  the  city  of  New  York.  This  cable  was  composed 
of  two  copper  wires  separately  wound  over  with  cotton, 
insulated  by  means  of  India-rubber,  and  inclosed  together 
in  a leaden  tube.  It  was  in  use  for  some  months,  after 
which  it  was  cut  through  by  the  ice. 

West,  in  the  year  1846,  applied  to  the  English  and 
French  Grovernments  for  permission  to  lay  down  a cable 
between  Dover  and  Calais,  and  carried  out  some  preliminary 
experiments  in  Portsmouth  Harbor  in  the  presence  of  a large 
number  of  spectators. 

In  1848  Armstrong  made  some  further  experiments  of 
the  same  kind  in  the  Hudson  River,  and  suggested,  in  an 
article  published  in  one  of  the  New  York  papers,  that 
a similar  cable  should  be  laid  across  the  Atlantic. 

Werner  Siemens  in  the  same  year  carried  out  some  ex- 
periments on  the  explosion  of  torpedoes  by  means  of  sub- 
merged electric  cables  in  Kiel  Harbor;  and  Walker  in  1849 


152 


ELECTRICITY  IN  MODERN  LIFE 


constructed  a cable,  consisting  of  copper  wire,  covered  with 
gutta-percha,  about  two  miles  in  length,  and  laid  it  out  into 
the  sea  from  Folkestone.  This  cable  was  connected  with 
the  overland  line  from  London  to  Folkestone,  and  messages 
were  sent  by  it  between  London  and  Mr.  Walker’s  yacht, 
two  miles  from  the  shore. 

In  the  meantime  Brett,  in  1847,  had  obtained  a conces- 
sion from  the  French  Government  for  laying  a cable  between 
England  and  France,  and  in  1849  a company  was  formed 
for  carrying  out  the  project.  A cable  twenty-five  nautical 
miles  in  length  was  manufactured.  It  was  made  of  copper 
wire  covered  with  gutta-percha,  and  was  constructed  in 
separate  lengths  of  one  hundred  yards,  which  were  joined 
by  twisting  the  ends  of  the  copper  wire  together  and  bind- 
ing them  over  with  gutta-percha  which  had  been  softened 
by  heating. 

This  cable  was  laid  in  August,  1850,  simultaneously 
from  Cape  Gris-nez  and  Dover,  the  cable  being  simply 
passed  overboard  from  drums  on  which  it  was  wound;  and 
leaden  weights  of  ten  or  twelve  pounds,  to  act  as  sinkers, 
were  fixed  at  intervals  of  about  one  hundred  yards.  When, 
however,  the  two  ends  were  joined  together  it  was  found 
that  the  cable  had  been  broken,  and  although  attempts  were 
made  to  take  it  up  and  repair  it,  they  were  unsuccessful, 
as  the  cable  was  not  strong  enough  to  lift  up  the  leaden 
weights  used  as  sinkers. 

The  original  concession  obtained  from  the  French  Gov- 
ernment expired  in  1850,  but  a further  extension  of  a year 
was  obtained.  The  failure  of  the  previous  attempts,  how- 
ever, had  made  capitalists  distrustful  of  the  project,  and 
if  it  had  not  been  for  Mr.  Crampton,  who  found  half  the 
capital  required  himself,  the  project  would  have  fallen 


SUBMARINE  TELEGRAPHS 


153 


through.  As  it  was,  however,  a cable  was  constructed  by 
Messrs.  Newall  & Oo. 

It  was  formed  of  four  copper  wires,  each  covered  with  a 
double  layer  of  gutta-percha.  These  were  twisted  together, 
and  the  intervals  filled  up  with  tarred  hemp,  after  which  it 
was  wound  over  with  tarred  cord,  and  the  whole  covered 
with  a set  of  ten  thick  iron  wires  wound  round  it  in  order 
to  protect  it  from  injury.  The  cable  was  laid  down  from 
Sangate,  but  the  weather  was  very  unfavorable,  so  that  the 
vessel  laying  it  was  unable  to  keep  her  course,  and  when 
the  whole  of  the  cable  was  paid  out,  she  was  still  about  a 
mile  from  the  French  shore.  Temporary  communication, 
however,  was  established  by  means  of  three  wires  simply 
covered  over  and  bound  together,  and  this  extemporized 
cable  was  afterward  replaced  by  means  of  a length  of  cable 
similar  to  the  rest,  and  in  November,  1851,  the  cable  was 
actually  opened  to  the  public,  and  since  then,  though  it  has 
frequently  been  repaired,  it  has  never  been  entirely  renewed. 

The  success  of  this  cable  restored  the  confidence  of 
capitalists,  and  an  attempt  was  soon  made  to  lay  a cable 
between  England  and  Ireland.  The  first  of  these  was  laid 
down  from  Holyhead  to  Howth,  the  cable  being  very  similar 
to  the  Dover  one,  but  the  insulation  was  bad,  so  that  when 
it  was  completed  it  was  found  that  signals  could  not  be 
transmitted,  and  attempts  were  made  to  pick  it  up  and 
mend  it;  they  were  not,  however,  successful.  Two  other 
attempts  were  rendered  unsuccessful,  by  the  vessel  laying 
the  cable  being  carried  out  of  her  course  by  currents;  but 
in  the  year  1853,  a large  cable  containing  several  conducting 
wires  was  laid  between  Portpatrick  and  Donaghadee. 

The  possibility  of  successful  submarine  cables  having 
now  been  completely  demonstrated,  there  was  no  difficulty 


164 


ELECTRICITY  IN  MODERN  LIFE 


in  obtaining  capital,  and  numerous  short  cables  were  laid 
down,  connecting  different  European  countries. 

In  the  meantime  the  success  of  the  second  attempt  to  lay 
a cable  between  Dover  and  Calais  had  resuscitated  the  idea 
of  establishing  electrical  communication  between  Europe 
and  America. 

In  the  year  1851,  Tebbets,  an  American,  and  Gisborne, 
an  English  engineer,  obtained  a series  of  concessions  from 
the  Government  of  Newfoundland,  and  formed  a company 
under  the  title  of  the  Electric  Telegraph  Company  of  New- 
foundland. This  company  laid  down  twelve  miles  of  cable 
between  Cape  Breton  and  Nova  Scotia,  but  as  it  was  unable 
to  carry  out  all  that  it  had  undertaken,  it  was  shortly  after- 
ward dissolved,  and  the  concessions  transferred  to  the 
Telegraphic  Company  of  New  York,  Newfoundland,  and 
London,  founded  by  Cyrus  W.  Field,  who,  in  1854,  obtained 
a further  concession,  giving  to  the  company  the  sole  right  of 
carrying  cables  to  Newfoundland  for  a period  of  fifty  years. 

A cable  eighty-five  miles  long  was  then  laid  between 
Cape  Breton  and  Newfoundland,  and  in  1856,  Field  came 
over  to  England  with  a view  of  raising  the  capital  for  laying 
a cable  between  Ireland  and  Newfoundland.  Here  he  asso- 
ciated himself  with  Brett,  Whitehouse,  and  Charles  Bright, 
who  founded  an  English  Company,  which  amalgamated 
with  the  American  one,  under  the  title  of  the  Atlantic 
Telegraph  Company. 

The  capital  of  this  company  was  provided  by  three  hun- 
dred and  forty-five  contributors,  who  subscribed  a thousand 
pounds  each.  Among  these  contributors  the  name  of  Mr. 
John  Pender,  now  Sir  John  Pender,  K.C.M.G.,  must  be 
specially  mentioned,  as  from  this  time  forth  he  practically 
took  the  lead  in  the  development  of  submarine  telegraphy. 


SUBMARINE  TELEGRAPHS  ’ 


155 


Before  the  new  cable  was  constructed,  a number  of  ex- 
periments were  made  by  Mr.  Whitehouse,  to  determine  the 
manner  in  which  the  rate  of  transmission  of  signals  depended 
on  the  length  of  the  cable;  and  he  found  that  the  time  re- 
quired for  the  transmission  of  a signal  increased  at  a some- 
what more  rapid  rate  than  the  length  of  the  line,  but  not 
in  proportion  to  the  square  of  the  length,  as  appeared  to 
be  indicated  by  the  theory  of  the  subject,  which,  however, 
was  at  that  time  quite  in  its  infancy. 

In  the  course  of  these  experiments,  Whitehouse  made 
the  very  important  discovery  that  the  rate  of  signalling 
could  be  increased  in  the  ratio  of  about  three  to  one,  by 
making  the  currents  flow  through  the  cable  in  opposite  direc- 
tions alternately,  instead  of  always  in  the  same  direction. 

As  the  Atlantic  cable  would  be  nearly  two  thousand 
miles  in  length,  it  was  thought  advisable,  before  incurring 
the  expense  of  having  it  constructed  and  laid  down,  to  obtain 
definite  experimental  evidence  of  the  possibility  of  trans- 
mitting signals  over  so  long  a line. 

Accordingly,  in  October,  1856,  Whitehouse  and  Bright 
connected  up  a series  of  existing  submarine  cables  with  the 
subterranean  line  between  London  and  Manchester,  and 
in  this  way  made  up  a circuit  of  about  two  thousand  miles 
in  length,  and  it  was  found  that  from  about  210  to  240  dis- 
tinct signals  could  be  sent  over  this  circuit  in  a minute,  and 
therefore  the  commercial  practicability  of  using  the  line, 
if  it  could  be  constructed  and  laid  successfully,  was  con- 
clusively demonstrated. 

The  core  of  the  cable  was  made  by  the  Guttapercha  Com- 
pany, of  Silvertown,  and  consisted  of  seven  copper  wires, 
covered  with  three  layers  of  gutta-percha.  The  core  was 
covered  with  hemp  soaked  in  a composition  of  Norwegian 


156 


ELECTRICITY  IN  MODERN  LIFE 


tar,  pitch,  linseed  oil,  and  wax,  and  was  protected  outside 
by  means  of  eighteen  ropes,  each  formed  of  seven  iron 
wires.  The  covering  was  manufactured  and  laid  on  by 
Messrs.  Glass,  Elliot  & Co.,  and  Messrs.  Newall  & Co. 

The  shore  ends  of  the  cables  were  protected  by  a much 
heavier  armor,  consisting  of  twelve  thick  iron  wires  twisted 
round  the  cable  in  a helical  form,  as  was  done  with  the  wire 
ropes  used  in  the  deep-sea  portions. 

Owing  to  the  absence  of  previous  experiments  on  the 
requirements  of  such  a cable,  and  also  to  the  haste  with 
which  its  manufacture  was  carried  out,  the  cable  was  un- 
fortunately exceedingly  defective,  and  Mr.  Whitehouse 
strongly  advised  its  rejection.  It  was,  however,  decided 
to  lay  it  down,  and  it  was  embarked  on  board  two  vessels — 
the  “Niagara,”  a vessel  of  five  thousand  tons,  belonging  to 
the  United  States  Navy,  and  the  “Agamemnon,”  an  English 
warship,  of  three  thousand  two  hundred  tons. 

It  was  decided  to  lay  the  cable  from  Valentia,  in  Ireland, 
to  Newfoundland,  as  the  ocean  bottom  between  these  two 
places  had  been  explored  by  Captain  Maury,  of  the  United 
States  Navy,  and  found  to  consist  of  a gently  undulating 
plateau,  covered  with  fine  mud,  usually  known  by  the  name 
of  Atlantic  ooze,  forming  a very  suitable  bed  for  the  cable. 

The  shore  end  of  the  cable  was  laid  down  from  V alentia 
by  means  of  two  smaller  vessels,  and  was  safely  effected  on 
the  6th  of  August,  1867.  On  the  following  day  the  shore 
end  was  joined  with  the  portion  on  board  the  “Niagara, ” 
and  the  paying  out  of  the  cable  went  on  successfully  until 
the  11th  of  August,  when,  after  a length  of  334  nautical 
miles  had  been  laid  down,  the  cable  broke,  owing  to  an 
accident  with  the  paying-out  machinery,  in  a depth  of  over 
2,000  fathoms  of  water.  Owing  to  this  accident  the  vessels 


SUBMARINE  TELEGRAPHS 


157 


returned  to  Plymouth,'  and  the  cables  were  landed  at  Key- 
ham,  and  stored  in  dry  tanks.  The  most  defective  portions 
were  there  replaced  by  new  ones,  and  an  additional  length 
of  750  miles  was  manufactured  by  Messrs.  Glass,  Elliot 
& Oo.  The  paying-out  machinery  was  also  very  greatly 
improved. 

This  time  it  was  decided  to  begin  laying  the  cable  in  mid- 
ocean by  the  two  vessels  simultaneously,  the  “Agamemnon” 
proceeding  toward  Valentia,  and  the  “Niagara”  toward 
Newfoundland.  Thb  cable  was  broken  several  times  in 
laying,  and  about  640  miles  of  it  were  lost,  but  at  last 
every  difficulty  was  overcome,  and  communication  estab- 
lished on  the  5th  of  August,  1858. 

It  was  found,  however,  that  the  signals  transmitted  by 
the  cable  gradually  became  less  distinct,  and  on  the  1st  of 
September  they  ceased  to  be  intelligible.  During  the  time 
that  communication  was  established  the  English  Government 
had  made  use  of  the  cable  to  send  a message  to  Canada, 
countermanding  the  departure  of  two  regiments  which  were 
about  to  return  to  England;  and,  as  they  would  have  had 
to  be  sent  back  again,  a considerable  expense  was  thereby 
saved  to  the  country.  This  was  a fortunate  circumstance, 
as  it  illustrated  in  a very  striking  manner  the  advantage  of 
establishing  telegraphic  communication  between  England 
and  America,  and  had  an  important  effect  in  encouraging 
further  attempts. 

Several  attempts  were  made  in  1860  to  pick  up  this 
cable,  but  they  were  all  unsuccessful.  The  Atlantic  Tele- 
graph Company  did  not,  however,  for  a moment  abandon 
their  hopes  of  success,  and  two  vessels  were  sent  out  to 
explore  the  ocean  bed  between  Ireland  and  Newfoundland. 
They  found  that  several  portions  of  the  bottom  where  the 


168 


ELECTRICITY  IN  MODERN  LIFE 


old  cable  had  been  laid  were  of  a rocky  character,  very 
likely  to  damage  the  cable,  and  a new  course  was  therefore 
marked  out  for  the  next  attempt,  about  twenty-seven  miles 
to  the  south  of  the  former  one,  the  positions  selected  for 
the  shore  ends  being  the  Bay  of  Heart’s  Content  in  New- 
foundland, and  Foilhommerum,  close  to  Valentia,  in  Ire- 
land. A new  cable  was  manufactured  by  the  Guttapercha 
Company,  the  core  having  been  designed  by  Messrs.  Glass, 
Elliot  & Co.  In  its  general  character  it  was  similar  to 
the  former  one,  but  the  construction  was  very  greatly 
improved. 

As  the  results  of  the  1857  expedition  had  shown  the 
inconvenience  of  employing  two  vessels  to  lay  the  cable 
simultaneously,  the  “Great  Eastern,”  of  22,500  tons,  was 
chartered  to  carry  the  entire  cable,  which  was  coiled  on 
board  in  three  immense  iron  tanks,  and  Captain,  now  Sir 
James,  Anderson  was  appointed  to  command  the  vessel, 
Mr.  Canning  being  engaged  as  engineer,  and  Professor, 
now  Sir  William,  Thomson  and  Mr.  F.  Varley  as  elec- 
tricians. The  Irish  shore  end,  which  had  been  made  by 
Henley  of  Woolwich,  was  laid  down  by  a smaller  vessel 
on  the  26th  of  July,  1865,  and  was  joined  to  the  main 
portion  on  board  the  “Great  Eastern”  on  the  following 
day,  when  the  process  of  paying  out  the  cable  was  at  once 
begun. 

On  the  24th  of  July,  after  84  miles  of  cable  had  been  laid 
down,  a fault  was  discovered  in  the  portion  which  had  been 
submerged,  and  ten  and  a half  miles  of  cable  had  to  be 
wound  in  before  the  fault  was  got  on  board,  when  it  was 
found  to  be  due  to  a small  piece  of  iron  which  had  pene- 
trated the  insulating  covering,  and  made  connection  between 
the  copper  core  and  the  water. 


SUBMARINE  TELEGRAPHS 


159 


A second  fault  occurred  wlien  716  miles  of  cable  bad 
been  laid  down,  and  this  also  was  successfully  repaired.  A 
third  fault  was  observed  on  the  2d  of  August,  after  1,186 
miles  of  cable  had  been  paid  out,  and  the  cable  had  to  be 
wound  in  from  a depth  of  about  two  thousand  fathoms. 
After  about  a mile  of  cable  had  been  recovered  an  acci- 
dent occurred  to  the  picking-up  machinery,  and  it  became 
necessary  to  stop  the  ship;  it  was  therefore  temporarily 
at  th.e  mercy  of  the  waves,  and  the  cable,  unable  to  bear 
the  strain  to  which  it  was  subjected,  parted  and  was  lost 
overboard. 

Several  attempts  were  made,  by  means  of  grapnels,  to 
pick  it  up ; but  although  the  engineers  succeeded  in  getting 
hold  of  the  cable,  the  tackle  was  not  strong  enough,  and 
gave  way  in  every  case  before  it  was  brought  to  the  sur- 
face. Ultimately,  the  attempts  had  to  be  abandoned,  as  all 
the  picking-up  tackle  was  exhausted.  This  disaster  ruined 
the  Atlantic  Company  financially,  and  there  appeared  very 
little  prospect  of  raising  the  capital  for  another  attempt;  for 
many  of  the  original  contributors  were  dead,  while  others 
had  began  to  despair  of  the  ultimate  success  of  the  project 
as  a commercial  enterprise,  and  preferred  the  certainty  of 
losing  what  they  had  already  put  into  it,  to  the  risk 
of  investing  further  capital  in  what  scarcely  seemed  more 
than  a forlorn  hope. 

This,  however,  was  fortunately  not  the  opinion  of  Mr. 
John  Pender  and  a few  others  who  shared  his  faith  in  the 
ultimate  success  of  the  enterprise;  and  the  Anglo-American 
Company  was  formed,  with  a capital  of  £600,000,  to  carry 
on  the  work  of  the  defunct  Atlantic  Company. 

The  first  object  of  the  new  company  was  to  lay  down 
a new  and  improved  cable;  and  the  second,  to  endeavor  to 


160 


ELECTRICITY  IN  MODERN  LIFE 


repair  and  complete  the  former  one.  Negotiations  for  the 
manufacture  of  a new  cable  were  therefore  opened  with 
Messrs.  Glass,  Elliot  & Co.,  and  with  the  Guttapercha 
Company;  but  the  latter  found  it  was  giving  up  much  of 
its  ordinary  business  in  order  to  carry  out  this  one  attempt, 
which,  if  it  were  unsuccessful,  might  involve  them  in  ruin, 
and  they  refused  to  proceed  with  the  work  unless  they 
received  a guarantee  amounting  to  a quarter  of  a million. 

Delay  at  this  moment  would  have  been  fatal  to  the 
project,  and  would  have  involved  the  loss  of  all  the  capi- 
tal, amounting  to  nearly  two  millions,  which  had  already 
been  expended;  but  when  Mr.  Pender  was  informed  by  the 
company  of  their  demand,  he  simply  asked  whether  his 
personal  guarantee  would  suffice;  and  on  being  told  that 
it  would,  he  at  once  gave  it,  and  the  work  was  put  in  hand 
forthwith. 

Another  cable  was  made  very  similar  to  the  former 
one,  except  that  the  iron  wire,  used  for  armoring  the 
cable,  was  galvanized  to  protect  it  from  the  disintegrating 
action  of  the  water. 

New  paying-out  and  picking-up  machinery  of  a greatly 
improved  type,  and  driven  by  an  engine  of  seventy  horse- 
power, was  placed  on  board  the  ''Great  Eastern’';  and  the 
"Medway”  and  "Albany,”  which  were  to  assist  the  "Great 
Eastern,”  were  provided  with  similar  machinery.  Two  ves- 
sels of  the  British  Navy,  the  "Terrible”  and  the  "Kac- 
coon,”  were  told  off  to  accompany  the  expedition,  and 
render  any  additional  assistance  that  might  be  required. 
The  shore-end  of  the  cable  was  laid  down  in  the  Bay  of 
Foilhommerum  on  the  7th  of  July,  1866,  and  on  the  13th 
the  junction  with  the  cable  stored  on  board  the  "Great 
Eastern”  was  effected,  and  the  latter  vessel  started  on  its 


SUBMARINE  TELEGRAPHS 


161 


voyage  to  Newfoundland,  where  it  arrived  on  the  27th  of 
July,  after  having  been  successful  in  laying  the  1,852  miles 
of  cable  without  any  mishap.  The  cable  was  laid  along  the 
line  previously  marked  out,  which  was,  as  already  stated, 
twenty-seven  miles  to  the  south  of  the  old  cable. 

On  the  9th  of  August  the  '‘Great  Eastern,”  accompanied 
by  the  "Medway,”  put  to  sea  to  endeavor  to  find  and  pick 
up  the  old  cable,  and  three  days  later  they  met  the  "Terri- 
ble” and  the  "Albany,”  which  had  been  despatched  eigh- 
teen days  earlier  to  endeavor,  in  the  first  place,  to  find,  by 
means  of  astronomical  observations,  the  place  where  the 
cable  had  been  abandoned;  and,  secondly,  to  begin  drag- 
ging for  it.  When  the  "Great  Eastern”  arrived,  the  "Al- 
bany” had  already  grappled  the  cable,  lifted  it  a certain 
distance,  and  supported  it  by  attaching  it  to  a buoy;  but 
the  chain  had  broken,  so  that  the  cable  had  fallen  back  to 
the  bottom,  carrying  with  it  about  two  thousand  fathoms 
of  chain.  Canning’s  plan  for  picking  up  the  cable  was  that 
the  "Great  Eastern,”  the  "Terrible,”  and  the  "Albany” 
should  drag  for  it  simultaneously,  and  when  they  had  grap- 
pled it,  and  lifted  it  to  a certain  height,  the  "Medway”  was 
to  cut  it  on  the  westerly  side,  so  as  to  allow  the  Valentia 
end  to  be  picked  up.  Several  times  the  vessel  succeeded 
in  getting  hold  of  the  cable,  and  once  it  was  brought  to 
the  surface,  but  it  slipped  out  of  the  grapnel  as  attempts 
were  being  made  to  attach  a chain  to  it.  At  last,  however, 
on  the  13th  of  August,  the  cable  was  grappled  and  lifted  to 
within  800  fathoms  of  the  surface,  when  the  chain  to  which 
the  grapnel  was  attached  was  fastened  to  a buoy.  The 
"Great  Eastern”  then  began  to  drag  three  miles  to  the 
west  of  the  buoy,  and  the  "Medway”  two  miles  to  the  west 
of  the  "Great  Eastern,”  and  both  vessels  succeeded  in  get- 


162 


ELECTRICITY  IN  MODERN  LIFE 


ting  hold  of  the  cable,  the  position  of  which  was  then  as 
shown  in  Fig.  39.  The  “Medway"’  then  cut  the  cable 
by  means  of  a cutting  grapnel  at  a depth  of  300  fathoms. 

The  part  grappled  by  the  “Great  Eastern”  was  then 
at  a depth  of  800  fathoms,  the  process  of  lifting  it  having 
been  stopped  at  that  depth,  as  the  strain  upon  the  grapnel 
had  risen  to  over  twenty  tons,  and  it  was  feared  that  any 
further  increase  would  cause  it  to  give  way.  When,  how- 
ever, the  cable  had  been  cut  by  the  “Medway,”  the  strain 
diminished  to  ten  or  eleven  tons,  and  the  “Great  Eastern” 
recommenced  the  work  of  picking  up.  It  was  got  on  board 
and  connected  with  the  electrical  instruments  on  the  2d  of 


September,  and  the  happy  result  was  immediately  signalled 
to  Yalentia.  The  extra  cable  which  had  been  provided  for 
repairing  the  old  one  was  then  joined  to  the  latter,  and  the 
“Great  Eastern”  began  laying  it  down  in  the  direction  of 
Newfoundland,  arriving  safely  at  the  Bay  of  Heart’s  Con- 
tent on  the  8th  of  September,  when  it  was  attached  to  the 
shore  end,  which  the  “Medway”  then  proceeded  to  lay 
down;  and  the  same  evening  communication  was  estab- 
lished through  it  between  Newfoundland  and  Yalentia. 
The  total  length  of  cable  laid  down  amounted  to  1,896 
miles. 

During  this  second  expedition  the  vessel  was  com- 


SUBMARINE  TELEGRAPHS 


163 


manded,  as  before,  by  Captain  Anderson,  and  Mr.  Can- 
ning directed  the  operations  of  laying  and  repairing,  while 
Professor  Thomson  and  Mr.  Willoughby  Smith  were  in 
charge  of  the  electrical  tests  on  board,  and  Mr.  Varley 
remained  at  Yalentia  to  superintend  the  testing  opera- 
tions there.  Since  the  successful  laying  of  the  Atlantic 
cable  in  1866,  new  cables  have  been  laid  down  in  grad- 
ually increasing  numbers  almost  every  year,  until  at  pres- 
ent they  form  a complete  network,  connecting,  in  conjunc- 
tion with  the  overland  telegraphs,  all  the  more  important 
places  in  the  civilized  world.  The  experience  thus  gained 
has  of  course  led  to  many  improvements  in  the  construc- 
tion of  the  cables,  in  the  methods  of  laying  them  down, 
and  picking  them  up  for  repairs,  and  in  the  apparatus 
used  for  transmitting  and  recording  signals. 

Cables  are  often  made  with  several  separate  conductors 
instead  of  only  one,  the  different  terminals  being  connected 
to  different  lines  on  shore;  but  whether  one  conductor  or  sev- 
eral are  employed,  each  of  them  is  now  invariably  made, 
not  of  a single  copper  wire,  but  of  several  wires,  usually 
three  or  seven,  as  this  is  found  to  entirely  obviate  the 
difficulty  arising  from  the  brittleness  of  solid  copper  wire, 
which  caused  a great  deal  of  trouble  in  the  earlier  cables, 
as  the  solid  wire  was  found  to  break  after  being  bent 
a few  times. 

The  covering  of  hemp  or  jute,  which  is  spun  round 
the  insulated  core  to  serve  as  a pad  or  protection  against 
the  pressure  of  the  iron  wires  forming  the  armor  of  the 
cable,  is  usually  known  as  the  ^'serving^ ' ; and  when  the 
cable  is  made  up  of  several  separate  conductors,  they 
are  usually  arranged  in  a circle  round  a central  core 
of  hemp  or  jute  known  as  the  worming.'' 


164 


ELECTRICITY  IN  MODERN  LIFE 


In  the  earlier  cables  both  the  serving  and  the  worming 
were  saturated  with  tar,  in  order  to  diminish  their  liability 
to  decay  in  the  water;  but  Mr.  Willoughby  Smith  found 
that  tar  temporarily  mended  small  defects  in  the  insulation, 
and  might  therefore  prevent  any  injury  to  the  core  from 
being  discovered  in  time  to  allow  of  its  being  repaired  before 
the  cable  was  laid  down ; while  it  was  not  a sufficiently  good 
insulator  to  mend  the  fault  permanently,  and  therefore  it 
is  now  no  longer  used,  the  hemp  being  tanned  instead. 
In  shallow  waters  submarine  telegraph  cables  are  very  liable 
to  injury,  either  from  anchors  dragging  over  them,  or  from 
their  being  chafed  against  a rocky  bottom;  or  again  from  the 
attacks  of  various  submarine  animals,  such  as  the  Teredos, 
which  will  bore  into  a cable  as  it  would  into  timber,  if  any 
portion  of  the  armor  is  removed  by  injury.  It  appears, 
however,  to  confine  itself  to  the  exposed  portions,  and  will 
not  bore  into  those  portions  of  the  hemp  which  lie  under- 
neath  the  iron  wires.  There  is  also  a case  on  record  of 
a swordfish  having  left  its  weapon  buried  in  the  insulating 
coating  of  a telegraph  cable. 

When  any  such  fault  occurs  its  presence  can  be  detected, 
and  its  position  ascertained,  by  electrical  tests  made,  either 
at  one  end  of  the  line,  or  at  both  ends  simultaneously,  with 
the  aid  of  adjustable  resistance  which  is  inserted  into  the 
circuit  between  the  end  of  the  cable  and  the  earth  connection. 

This  adjustable  resistance  consists  of  a series  of  coils, 
the  resistances  of  which  are  all  known  multiples  of  a definite 
unit,  usually  the  Legal  Ohm.  The  resistance  per  mile  of  the 
cable  is  known  from  tests  made  before  it  is  laid  down,  and 
when  a fault  occurs  the  electrical  tests  enable  the  resistance 
of  the  cable  between  the  fault  and  either  end  to  be  deter- 
mined, and  therefore  the  distance  along  the  cable  at  which 


SUBMARINE  TELEGRAPHS 


165 


the  fault  occurs  is  obtained  by  simply  dividing  the  total 
observed  resistance  by  the  resistance  of  a mile  of  the  cable. 

The  first  successfully-laid  Dover  and  Calais  cable,  and 
the  other  short  cables  which  were  laid  shortly  afterward, 
were  worked  by  means  of  needle  instruments,  or  other  ordi- 
nary telegraph  apparatus  then  in  use  on  overland  lines. 
None  of  these,  however,  was  sufficiently  delicate  to  give 
good  results  over  a great  length  of  cable,  and  they  were 
therefore  very  soon  displaced  by  the  mirror  galvanometer. 
It  has  already  been  mentioned  that  this  instrument  was 
originally  devised  by  Grauss  and  Weber,  and  employed  on 
their  telegraph  line  at  Gottingen.  It  was  subsequently  very 
much  improved  by  Sir  William  Thomson,  and  one  of  the 
instruments  made  by  him  was  employed  at  Yalentia  during 
the  few  weeks  that  communication  was  possible  through  the 
cable  of  1858. 

Thomson’s  astatic  reflecting  galvanometer,  now  employed 
for  submarine  cable  work,  consists  of  a pair  of  magnets  con- 
nected rigidly  together  in  such  a way  that  when  suspended 
by  a silk  fibre  they  will  hang  horizontal!}^  one  above  the 
other  with  similar  poles  pointing  in  opposite  directions. 
The  two  magnets  are  of  as  nearly  equal  strength  as  it  is 
possible  to  make  them,  so  that  when  placed  in  a magnetic 
field  the  directive  force  acting  on  them  is  very  much  weaker 
than  it  would  be  upon  a single  magnet  only.  The  magnetic 
field  is  usually  produced  by  means  of  a small  magnet  bent 
in  a vertical  plane  in  the  form  of  a circular  arc,  and  made 
to  slide  upon  an  upright  rod  attached  to  the  case  of  the 
instrument. 

This  is  more  convenient  than  using  the  earth’s  magnetic 
field,  because,  by  means  of  the  adjustable  magnet,  the  sus- 
pended magnets  can  be  made  to  turn  in  any  desired  direc- 


166 


ELECTRICITY  IN  MODERN  LIFE 


tion.  These  suspended  magnets  are  exceedingly  small  and 
light;  and  each  of  them  is  attached  to  the  back  of  a small 
mirror  formed  of  silvered  microscope  glass.  A very  large 
number  of  turns  of  exceedingly  fine  silk-covered  copper 
wire  are  then  wound  round  the  pair  of  suspended  magnets 
in  a coil  having  the  shape  and  position  of  a vertical  figure 
of  8.  The  result  of  this  is,  that  whatever  the  direction  of 
the  current  through  the  coil,  the  effect  of  the  portions  sur- 
rounding each  of  the  two  suspended  magnets  is  to  turn  them 
both  in  the  same  direction. 

The  resistance  of  a galvanometer  of  this  kind  is  very 
high,  generally  from  seven  thousand  Ohms  upward,  but  this 
does  not  produce  any  sensible  diminution  in  the  strength 
of  the  current,  which  by  Ohm’s  law  is  equal  to  the  electro- 
motive force  divided  by  the  total  resistance,  because  the 
resistance  of  the  cable  is  so  great  that  the  galvanometer 
resistance  does  not  increase  it  by  any  perceptible  proportion 
of  the  whole. 

The  object  of  using  exceedingly  fine  wire  is  to  enable 
a very  large  number  of  turns  to  be  wound  in  very  close 
proximity  to  the  suspended  magnet,  in  order  to  magnify 
as  much  as  possible  the  effect  of  the  weak  current  passing 
through  the  cable. 

In  reading  a message  by  means  of  the  mirror  galvanom- 
eter, it  is  placed  close  to  the  observer ; and  opposite  to  it, 
at  a considerable  distance,  is  placed  a horizontal  scale,  at  the 
centre  of  which  is  a small  vertical  slit.  A lamp  is  placed 
beyond  this  slit,  and  its  rays,  concentrated  by  means  of 
a lens,  are  allowed  to  fall  upon  the  mirror,  and  reflected 
back  upon  the  scale.  The  observer  watches  the  motion  of 
the  spot  of  light  upon  the  scale,  and  the  reader  will  easily 
see  that  a very  small  motion  of  the  mirror  will  be  sufficient 


SUBMARINE  TELEGRAPHS 


167 


to  give  a perfectly  perceptible  motion  to  the  spot  of  light. 
The  dots  and  dashes  of  the  Morse  code  are  indicated  by 
motions  to  the  right  and  left  respectively  of  the  centre 
of  the  scale. 

It  is  exceedingly  fatiguing  to  the  eye  to  watch  the  mo- 
tion of  the  spot  of  light  in  the  mirror  galvanometer  for  any 
length  of  time,  and  although  the  instrument  is  still  largely 
employed  for  making  electrical  tests,  it  has  been  to  a great 
extent  superseded  for  signalling  purposes  by  the  “Siphon” 
recorder,  a most  beautiful  and  ingenious  instrument,  which 
is  also  the  invention  of  Sir  William  Thomson.  The  construc- 
tion of  this  instrument  is  far  too  complicated  for  me  to  tax 
my  readers’  patience  by  describing  it  in  detail,  but  its  gen- 
eral principle  is  very  easily  understood. 

A flat  coil  of  very  thin  wire,  in  circuit  with  the  line, 
is  suspended  by  means  of  silk  fibres  between  the  poles  of 
a powerful  electro-magnet,  in  such  a way  that  when  no  cur- 
rent is  passing  through  it,  it  hangs  with  its  plane  vertical 
and  passing  through  the  line  joining  the  poles  of  the  electro- 
magnet. When  a current  is  sent  through  the  suspended 
coil  the  latter  behaves  like  a magnet,  just  as  in  Ampbre’s 
experiments,  and  tries  to  set  itself  with  its  plane  perpen- 
dicular to  the  line  joining  the  poles  of  the  electro-magnet. 
The  suspended  coil  is  made  to  communicate  its  motions  by 
means  of  fine  silk  fibres  to  a very  fine  glass  siphon,  one  end 
of  which  dips  into  an  insulated  metallic  vessel  containing 
ink,  while  the  other  extremity  rests,  when  no  current  is 
passing,  just  over  the  centre  of  a paper  ribbon  which  can 
be  carried  underneath  it  by  means  of  clockwork.  When 
the  instrument  is  to  be  used,  the  vessel  of  ink  is  connected 
with  an  electrically  charged  conductor,  the  effect  of  which 

is  to  drive  the  ink  out  of  the  siphon  in  small  drops.  The 

Science — Yol.  XIII — 8 


168 


ELECTRICITY  IN  MODERN  LIFE 


clockwork  is  at  the  same  time  set  in  motion,  the  result  being 
to  draw  a fine  dotted  line  aloDg  the  centre  of  the  ribbon. 

When  currents  are  sent  through  the  line  the  point  of  the 
siphon  moves  alternately  above  and  below  the  line,  drawing 
a wavy  instead  of  a straight  line,  and  this  wavy  line  gives 
a permanent  record  of  the  message,  the  motion  of  the  siphon 
above  the  central  line  corresponding  to  the  dots  of  the  Morse 
code,  and  its  motion  in  the  other  direction  corresponding 
to  the  dashes.  It  has  already  been  mentioned  that  White- 
house  found  in  his  experiments,  preliminary  to  the  first 
attempt  to  lay  an  Atlantic  cable,  that  the  rapidity  of  signal- 
ling could  be  greatly  increased  by  sending  currents  alter- 
nately in  opposite  directions  through  the  line.  This  he 
himself  attempted  to  effect  by  the  use  of  a small  magneto 
machine,  but  a more  satisfactory  method  is  to  alternately 
connect  the  copper  and  zinc  poles  of  the  battery  at  the 
transmitting  station  with  the  cable,  the  end  not  in  connec- 
tion with  the  cable  being  at  the  same  moment  put  to  earth. 
In  order  to  obtain  the  best  effects,  the  duration  of  the 
different  currents  in  opposite  directions  should  bear  definite 
ratios  to  one  another,  depending  of  course  on  the  succession 
of  signals  to  be  sent.  It  is  very  difficult  to  do  this  satisfac- 
torily with  any  form  of  key  operated  by  hand,  but  it  is  done 
most  effectively  by  means  of  the  automatic  curb  transmitter, 
an  instrument  devised  by  Sir  William  Thomson  for  use 
with  the  siphon  recorder,  and  which  automatically  makes, 
breaks,  and  reverses  the  contacts  as  required,  under  the 
guidance  of  a strip  of  punched  paper  similar  to  that  em- 
ployed with  the  Wheatstone  automatic  transmitter,  which 
was  described  in  the  last  chapter. 


THE  TELEPHONE 


169 


CHAPTEE  XII 

THE  TELEPHONE 

The  first  recorded  attempt  to  transmit  speech  by  elec- 
tricity was  made  by  Philipp  Eeis,  a German  school- 
master, who  began  his  researches  in  the  year  1860. 
His  first  transmitter  was  formed  out  of  the  bung  of  a beer- 
barrel,  hollowed  out,  and  having  one  end  closed  with  the  skin 


of  a German  sausage  to  serve  as  a membrane.  A somewhat 
less  primitive  form  of  the  instrument  is  shown  in  Fig.  40. 
It  consisted  of  a cube  of  wood,  hollowed  out  in  a conical 
form,  and  having  the  smaller  end  of  this  hollow  closed  with 
a very  fine  stretched  membrane.  A narrow  springy  strip  of 
platinum  foil  was  attached  to  the  upper  binding  screw,  as 


170 


ELECTRICITY  IN  MODERN  LIFE 


shown  in.  the  diagram,  while  its  lower  end  rested  against 
the  centre  of  the  membrane.  A second  platinum  strip, 
provided  with  a contact  point,  was  attached  to  the  lower 
binding  screw,  and,  by  means  of  the  adjusting  .screw  shown 
in  the  illustration,  was  made  to  just  touch  the  lower  end 
of  the  first  platinum  strip. 

The  two  binding  screws  were  placed  in  circuit  with  the 
battery  and  with  the  line  through  which  messages  were  to 
be  sent.  Eeis’s  original  receiver,  shown  in  Fig.  41,  con- 
sisted simply  of  a violin,  upon  the  bridge  of  which  was 
stuck  upright  a knitting-needle,  surrounded  by  a coil  of 

silk-covered  copper  wire.  If 
a musical  note  was  sounded 
opposite  the  larger  end  of  the 
hollow  of  the  transmitter,  the 
membrane  was  thrown  into 
vibration,  making  and  break- 
ing the  circuit  once  at  each 
complete  vibration.  As  often 
as  the  circuit  was  completed 
the  knitting-needle  was  mag- 
netized by  the  coil  surrounding  it,  and  demagnetized  when 
the  current  was  broken.  Now,  it  was  explained  in  a former 
chapter  that  when  a piece  of  iron  is  suddenly  magnetized  or 
demagnetized  a slight  sound  is  heard,  and  as  the  number 
of  magnetizations  and  demagnetizations  in  a second  was 
equal  to  the  number  of  vibrations  corresponding  to  the  note 
sounded  at  the  transmitter,  the  result  was  that  the  note  was 
reproduced.  Reis  attempted  to  use  his  instrument  for  trans- 
mitting words  spoken  into  the  transmitter,  but  he  does  not 
seem  to  have  been  able  to  do  more  than  occasionally  reproduce 
a single  syllable  or  short  word,  and  that  very  indistinctly. 


THE  TELEPHONE 


171 


We  now  know  that  the  reason  of  this  was  that  the 
sounds  emitted  by  the  human  voice  are  of  much  too  com- 
plicated a nature  to  be  reproduced  by  any  apparatus  which 
simply  makes  and  breaks  the  circuit,  and  although  Profes- 
sor S.  P.  Thompson  has  been  more  or  less  successful  in 
transmitting  articulate  sounds  by  means  of  instruments  of 
similar  construction  to  those  of  Eeis,  it  has  only  been  by 
very  carefully  adjusting  the  contact-breaking  spring,  and 
speaking  to  it  very  softly,  so  as  only  to  vary  the  pressure 


Fig.  42. 


between  the  two  platinum  surfaces  instead  of  actually  break- 
ing the  contact.  Eeis  made  a great  number  of  other  trans- 
mitters of  an  imperfect  form,  one  of  which  is  shown  in 
Fig.  42.  It  consisted  of  a double  electro-magnet  about  six 
inches  in  length,  laid  horizontally  upon  a wooden  sound- 
ing-board. In  front  of  the  poles  of  the  electro-magnet  was 
placed  an  iron  rod  of  elliptical  section,  attached  to  a 
wooden  lath  supported  on  a cross  wire,  and  capable  of 
having  its  position  regulated  by  means  of  the  upper  adjust- 
ing screw,  and  a tension  spring  attached,  as  shown,  to  the 
lower  screw  in  the  illustration. 


172 


ELECTRICITY  IN  MODERN  LIFE 


It  is  curious  that  though  Eeis-  provided  his  transmitters 
with  elaborate  mouthpieces,  he  never  attempted  anything 
of  the  kind  for  the  receiver,  although  subsequent  experi- 
ments have  shown  that  it  is  a much  more  important  feature 
in  the  latter  case  than  in  the  former. 

The  first  speaking  telephone  was  the  invention  of  Alex- 
ander Graham  Bell,  a Scotchman  who  had  settled  in  the 
United  States  and  become  a naturalized  American  citizen. 

The  first  telephones  constructed  by  Bell  were  not  speak- 
ing ones,  and  one  of  these  earlier  forms  is  shown  in  Fig.  43. 
The  same  instrument  served  either  for  transmitting  or  re- 


Fig.  43. 


ceiving  the  message,  and  consisted  of  a pair  of  harps  formed 
of  steel  rods  attached  to  the  poles  of  a permanent  magnet, 
NS,  and  having  their  free  ends  respectively  above  and 
below  the  soft  iron  core  of  an  electro-magnet,  E. 

Two  such  instruments  are  shown  in  the  diagram  con- 
nected up  ready  for  use;  one  end  of  the  coil  of  each  electro- 
magnet is  earth-connected,  and  the  other  two  ends  are 
connected  with  each  other  through  the  line. 

If  one  of  the  bars  of  the  harp  H is  thrown  into  vibration 
mechanically,  or  by  singing  to  it  or  playing  a musical  note 
in  its  neighborhood,  it  will  send  an  undulatory  current,  of 
a period  corresponding  to  that  of  the  note,  through  the  line, 


THE  TELEPHONE 


173 


and  this  will  set  in  vibration  the  corresponding  rod  of  the 
harp  H — that  is  to  say,  the  rod  giving  the  same  note  as  that 
which  was  sounded  at  the  transmitting  station;  the  reason 
that  one  of  the  rods  will  respond  to  a note  sounded  near 
it  is  that  its  period  of  vibration  is  equal  to  the  period  of  the 
note,  so  that  the  successive  impulses  caused  by  the  waves 
striking  the  rod  all  tend  to  increase  the  vibration  instead 
of  counteracting  each  other’s  effects.  A familiar  example  of 
exactly  the  same  phenomenon  is  given  by  the  well-known 
fact  that  if  the  sounding-board  of  a piano  is  lifted  and 
a certain  note  sung  above  the  strings,  it  will  be  taken  up 
by  the  string  giving  the  same  note.  The  study  of  the  notes 
required  to  produce  the  different  vowel  sounds  shows  that 
if  a piano  were  made  with  a sufficient  number  of  strings 
to  each  octave,  or  a harp  such  as  that  used  by  Bell  with 
a sufficient  number  of  rods,  vowel  signs  could  be  perfectly 
reproduced  by  setting  them  in  vibration  one  after  another. 
Bell  pursued  this  idea  for  some  time,  as  he  thought  it  might 
give  a convenient  means  of  sending  a number  of  messages 
simultaneously  along  the  same  line.  This  was  to  be  effected 

by  a pair  of  notes  being  selected  for  each  pair  of  instru- 

% 

ments,  to  give  signals  corresponding  to  dots  and  dashes 
respectively,  a different  pair  of  notes  being  used  for  each 
such  pair  of  instruments. 

The  clerk  at  the  transmitting  station  would  simply  have, 
by  means  of  a suitable  key,  to  set  his  pair  of  rods  in  vibra- 
tion in  the  proper  manner  to  transmit  a message.  At  each 
receiving  station  a number  of  the  rods  actuated  by  the  send- 
ing instruments  would  be  vibrating  together,  but  it  was  sup- 
posed that  each  clerk  would  be  able  to  pick  out  the  two 
notes  which  it  was  his  business  to  attend  to,  and  to  train 
his  ears  so  as  to  distiuguish  these  while  neglecting  the 


174 


ELECTRICITY  IN  MODERN  LIFE 


others.  The  plan  might  possibly  be  a success  if  telegraph 
clerks  invariably  possessed  accurately  trained  musical  ears, 
but  unfortunately  comparatively  few  persons  possess  the 
power  of  training  their  ears  to  the  extent  which  would 
be  necessary. 

After  a long  series  of  experiments,  the  transmitter 

shown  in  Fig.  44,  and  the 
receiver  shown  in  Fig.  45, 
were  constructed,  and  these 
are  of  special  interest  as  be- 
ing the  first  pair  of  instru- 
ments that  could  really  be 
said  to  form  a speaking 
telephone.  They  were  exhibited  in  Philadelphia  in  1876, 
and  at  the  meeting  of  the  British  Association  in  the  same 
year.  Sir  William  Thomson  excited  a widespread  interest 
by  exhibiting  this  receiver  to  the  meeting  at  Glasgow,  and 

giving  an  account  of  the  re- 
sults obtained  by  Mr.  Bell  in 
the  same  year. 

The  first  public  exhibition 

# 

of  the  speaking  telephone  in 
England  was  given  by  Mr. 
Preece  at  the  Plymouth  meet- 
ing of  the  British  Association 
in  1877,  when  the  Glasgow  re- 
ceiver had  been  abandoned,  and  the  transmitter  modified 
into  a form  not  differing  greatly  from  that  shown  in  Fig.  46, 
which  represents  the  Bell  receiver  now  in  use,  and  which 
was  used  for  some  time  both  as  receiver  and  transmitter. 
It  consists  of  a case  made  of  wood  or  ebonite,  the  latter 
being  now  almost  universally  employed,  containing  a per- 


THE  TELEPHONE 


175 


manent  steel  magnet,  a,  opposite  which  is  a vibrating  plate, 
pp^  made  of  thin  steel. 

The  distance  between  the  magnet  and  the  plate  can  be 
adjusted  by  means  of  the  screw,  d.  On  the  N end  of  the 
magnet  is  placed  a small  boxwood  reel,  hb^  wound  with  silk- 
covered  copper  wire,  the  ends  of  which  are  connected  by 
means  of  the  terminals,  M,  with  the  line  LS.  The  mouth- 
piece, FF,  is  fastened  by  means  of  two  screws,  to  the 
projecting  flange  UU^  of  the  case,  and  holds  the  vibrating 
diaphragm  in  position.  This  diaphragm  is  made  of  a ferro- 
type  plate  such  as  that  used  by  photographers,  which  gives 


Fig.  46. 

a much  clearer  intonation  than  the  membranes  employed  in 
the  earlier  instruments.  The  principle  of  these  instruments 
is  similar  to  that  of  the  harp  telephone  first  made  by  Bell, 
except  that  the  harp,  which  can  only  produce  a limited  num- 
ber of  definite  notes,  is  replaced  by  the  steel  diaphragm, 
which  reproduces  with  more  or  less  clearness  all  the  notes 
which  go  to  make  up  the  human  voice. 

As  in  the  former  instrument,  no  battery  is  required,  the 
undulatory  current  being  produced  by  the  vibrations  of 
the  diaphragm  spoken  to,  and  reproducing  the  sound  in 
the  receiving  instrument,  by  setting  up  vibrations  in  its 
diaphragm,  synchronous  with  those  of  the  first. 


176 


ELECTRICITY  IN  MODERN  LIFE 


The  next  advance  in  telephony  was  made  by  Edison’s 
invention  of  the  carbon  transmitter.  This  instrument,  which 
is  shown  in  Fig.  47,  was  based  on  the  discovery,  made  by 
Du  Moncel  in  1866,  that  an  increase  of  pressure  between 
two  conductors  in  contact  causes  a diminution  in  the  elec- 
trical resistance  of  the  circuit  of  which  they  form  a part. 
B is  an  ebonite  mouthpiece,  D a vibrating  plate,  and  I a 
disk  of  prepared  carbon  about  the  size  of  a shilling,  the 
distance  of  which  from  the  vibrating  plate  can  be  adjusted 
by  means  of  the  screw,  F.  A small  platinum  plate,  B, 
carrying  a rounded  ivory  button,  5,  is  fixed  to  the  upper 


Fig.  47. 


surface  of  the  carbon  disk.  When  the  membrane  is  set  in 
vibration  by  speaking  to  it,  the  vibrations  are  communicated 
to  the  carbon  by  means  of  the  small  platinum  plate;  and  the 
variations  of  pressure  produced  in  this  way  cause  a variation 
in  the  electrical  resistance  of  the  contact,  and  therefore  set 
up  a series  of  undulations  in  a battery  current  made  to 
traverse  the  circuit.  In  practice  it  is  found  better,  when 
using  the  carbon  transmitter,  not  to  place  the  receiver  in 
circuit  with  the  battery  and  transmitter,  but  to  allow  the 
undulatory  current  from  the  latter  to  traverse  the  primary 
wire  of  a small  induction  coil,  and  to  place  the  receiver  in 
circuit  with  the  secondary  wire  of  the  same  coil,  in  which 


THE  TELEPHONE 


177 


undulatory  currents  are  produced  by  the  inductive  action 
of  the  original  current. 

In  the  same  year  that  Edison  devised  the  carbon  trans- 
mitter, Mr.  Hughes  read  a paper  before  the  Eoyal  Society 
in  which  he  described  an  instrument  of  a very  similar  char- 
acter, to  which  he  gave  the  name  of  the  “microphone.” 
A simple  and  efficient  form  of  this  instrument  is  shown 
in  Fig.  48,  and  consists  of  a pencil  of  gas  carbon  (viz.,  the 
residue  left  in  a gas  retort  when  the  gas  has  been  expelled 


from  the  coal)  pointed  at  each  end  and  resting  in  cups,  CC, 
of  a similar  material.  When  this  instrument  is  connected 
through  a battery,  B,  with  a circuit,  XY,  containing  a tele- 
phone, it  is  found  to  act  as  a very  powerful  telephone  trans- 
mitter, and  the  slightest  touch  against  the  pencil  will  pro- 
duce a grinding  noise  in  the  telephone.  If  the  instrument 
is  allowed  to  rest  on  a small  wooden  match-box  in  which 
a fly  is  walking,  the  noise  produced  by  its  motions  can 
be  distinctly  heard  in  a telephone  in  circuit  with  the 
microphone. 


178 


ELECTRICITY  IN  MODERN  LIFE 


A large  number  of  carbon  transmitters  of  various  kinds 
have  been  devised  by  different  inventors,  all  of  them  modifi- 
cations, not  of  Edison’s  transmitter,  but  of  Hughes’s  micro- 
phone. Of  these  it  will  be  sufficient  to  describe  the  Blake 
transmitter,  which  is  the  one  universally  used  in  connection 
with  the  telephone  exchanges  in  Great  Britain.  It  consists 
of  a small  wooden  frame,  H,  Fig.  49,  hollowed  out  in  the 
centre  so  as  to  form  a mouthpiece,  a,  and  carrying  on  its 

reverse  side  an  iron  ring,  rr,  Fig.  60,  to 
which  are  screwed  two  pieces,  oppo- 
site to  each  other.  These  are  connected 
by  the  conducting  rail  c,  which  is  kept 
in  position  by  means  of  the  brass  plate  m 
and  the  screw  n.  The  iron  diaphragm  e 
is  placed  immediately  behind  the  funnel- 
shaped  mouthpiece  a.  Between  the  dia- 
phragm and  the  vertical  rail  c,  the  upper 
part  of  which  is  bent  at  right  angles, 
there  is  an  interval  of  about  three- 
quarters  of  an  inch. 

A strip  of  insulating  material,  i,  car- 
ries a thin  flexible  steel  spring,  /,  the 
lower  end  of  which  terminates  in  a 
small  platinum  button  pressing  on  one 
diaphragm,  and  on  the  other  against  a 
small  carbon  disk,  k,  fastened  to  a small  brass  plate,  p. 
The  latter  is  fastened  to  the  lower  end  of  a flat  spring, 
the  upper  end  of  which  is  fixed,  as  shown,  to  the 
shorter  arm  of  c.  The  spring  g is  coated  with  gum,  and 
is  only  in  electrical  connection  with  the  spring  / by  means 
of  the  platinum  contact.  The  diaphragm  e is  contained  in 
the  India-rubber  ring  u.  Fig.  50,  and  is  kept  in  position 


Fia.  49. 

side  against  the 


THE  TELEPHONE 


179 


by  the  springs  w'  which  are  screwed  to  the  ring  r.  The 
frame  H forms  the  door  of  a small  case  containing  the 
induction  coil,  E.  The  current  passes  from  one  pole  of 
the  battery,  through  the  primary  coil,  over  the  ring  r,  the 


upper  piece  6,  the  brass  plate  m,  the  upper  arm  of  the  rail 
c,  the  spring  the  brass  plate  p,  the  carbon  disk  and 
the  platinum  contact  of  the  spring  /,  back  to  the  other  pole 
of  the  battery,  the  secondary  coil  being  placed,  as  before 


180 


ELECTRICITY  IN  MODERN  LIFE 


explained,  in  circuit  with  the  line  and  receiver.  When  the 
diaphragm  e is  thrown  into  vibration,  the  vibrations  are 
transferred  to  the  spring  /,  causing  a variation  in  the  press- 
ure between  the  platinum  contact  and  the  carbon  disk  h. 

According  to  Mr.  Preece,  from  whose  book  on  the  tele- 
phone the  above  description  is  taken,  the  articulation  of  this 
instrument  is  inferior  to  that  of  many  others  for  long  dis- 
tances, although  for  short  distances  it  is  very  good.  Before 
proceeding  to  give  an  account  of  the  manner  in  which  the 
telephone  is  employed  in  commercial  and  every-day  life, 
it  will  be  of  interest  to  notice  briefly  some  special  forms  of 
telephonic  apparatus. 

Edison's  Loud-Speaking  Telephone. — This  instrument  is  a 
most  ingenious  form  of  telephone  receiver  based  upon  the 
discovery  made  by  the  inventor  that  if  a metallic  plate  were 
allowed  to  slide  over  certain  prepared  surfaces,  such  as 
chalk  moistened  with  an  easily  decomposed  electrolyte  like 
potassic  iodide,  the  frictional  resistance  to  sliding  could 
be  very  greatly  diminished  by  passing  a current  through 
the  contact.  The  instrument  is  shown  in  Pig.  51.  A is  a 
chalk  cylinder,  which  can  be  turned  at  a regular  speed 
by  a set  of  multiplying  wheels  driven  by  the  handle  W. 
C is  a strip  of  platinum  supported  by  a thin  mica  diaphragm, 
and  made  to  press  with  a constant  pressure  against  the 
cylinder  by  the  spring  S,  which  is  capable  of  adjustment 
by  the  screw  E.  The  current  from  the  transmitter  flows 
through  the  support  H to  the  chalk  cylinder  A,  and  thence 
through  the  platinum  strip  0 and  the  wire  D to  earth. 

When  the  cylinder  is  made  to  rotate,  the  friction  between 
it  and  the  strip  0 displaces  the  latter  in  the  direction  of 
motion,  the  displacement  being  greater  the  greater  the 
friction. 


THE  TELEPHONE 


181 


Every  variation  in  the  undulatory  current,  sent  through 
the  contact  by  means  of  the  transmitter,  will  produce  a cor- 
responding variation  in  the  friction,  causing  the  mica  disk 
to  vibrate  in  exact  synchronism  with  the  diaphragm  of  the 
transmitter.  Instruments  of  this  type  were  at  one  time  sup- 
plied for  use  in  private  houses,  but  although  they  spoke 
much  more  loudly  than  the  ordinary  Bell  receivers,  they 
were  found  exceedingly  troublesome,  because  the  cylinder, 


in  order  to  work  satisfactorily,  must  be  neither  wet  nor  dry, 
but  only  just  moist,  and  therefore  requires  very  careful 
attention.  It  acts  best  when  it  has  been  slightly  moistened 
with  a camel-hair  brush  from  twelve  to  twenty-four  hours 
before  using  it.  To  get  really  good  results  with  this  ap- 
paratus it  is  essential  that  the  cylinder  should  be  made 
to  rotate  with  uniform  velocity.  This  can  be  effected  much 
more  satisfactorily  by  means  of  clockwork  than  by  hand. 


182 


ELECTRICITY  IN  MODERN  LIFE 


but  as  the  clockwork  requires  heavy  weights  to  drive  it, 
such  an  apparatus  is  more  suited  for  exhibition  than  for 
practical  use.  When  carefully  adjusted,  its  reproduction 
of  speech  and  musical  sounds  is  very  loud  and  distinct. 
It  may  be  of  interest  to  illustrate  this  by  describing  some 
of  the  results  which  I obtained  when  using  a very  fine 
instrument  of  this  character,  which  had  been  loaned  by 
the  United  Telephone  Company  for  a lecture  on  the  Tele- 
phone, delivered  in  the  schoolroom  attached  to  a church 
in  Kensington.  The  telephone  company  had,  in  addition 
to  lending  this  and  other  apparatus,  kindly  connected  the 
schoolroom  for  the  evening  with  their  exchange  system, 
and  in  the  course  of  the  evening  communication  was  estab- 
lished between  the  lecture-room  and  the  telephone  exchange 
at  Brighton.  The  loud-speaking  telephone  was  placed  on 
its  stand  in  front  of  the  platform,  and  stood  about  five  feet 
above  the  ground.  A cornet-player  had  been  sent  down  to 
Brighton,  and  played  his  cornet  opposite  a carbon  trans- 
mitter of  a form  somewhat  different  from  either  of  those 
described,  and  more  suitable  for  the  transmission  of  the 
musical  notes,  which  were  reproduced  by  the  Edison  instru- 
ment with  the  greatest  clearness,  and  so  loudly  as  to  be 
heard  in  every  part  of  the  lecture-hall.  The  voice  of  the 
speaker  at  the  Brighton  exchange  was  also  very  clearly 
reproduced;  and  although  the  reproduction  was  not  so  loud 
as  in  the  case  of  the  cornet,  the  words  spoken  were  heard 
distinctly  at  a distance  from  twenty  to  thirty  feet  from  the 
instrument. 

The  Photophone, — In  the  year  1873  Mr.  Willoughby 
Smith  discovered  that  when  selenium  was  exposed  to 
light  its  electrical  resistance  varied  with  the  intensity 
of  the  light  falling  upon  it,  and  shortly  afterward  Pro- 


THE  TELEPHONE 


183 


fessor  W.  G.  Adams  found  that  a ray  of  light  falling  upon 
a bar  of  selenium  produced  an  E.M.F.,  causing  the  selenium 
under  the  influence  of  light  to  act  like  a small  battery.  Mr. 
Graham  Bell  and  Mr.  Tainter,  after  a long  series  of  experi- 
ments, succeeded  in  constructing  an  apparatus  in  which  this 
property  of  selenium  was  utilized  for  the  reproduction  of 
sound  at  a distance  by  the  aid  of  luminous  rays.  The 
transmitter  and  receiver  in  their  latest  form  are  shown  in 
Figs.  52  and  53.  The  transmitter,  Fig.  52,  consists  of  a 
simple  telephonic  box,  B,  provided  with  a mouthpiece  and 


Transmitter 


Fig.  52. 


Receiver 


C 


Pig.  53. 


a membrane  of  mica  plated  with  silver,  forming  a mirror 
on  which  rays  of  light  are  directed  by  means  of  an  arrange- 
ment of  mirrors  and  lenses,  such  as  M,  L,  A in  the  diagram, 
from  some  powerful  source,  such  as  an  electric  lamp,  or, 
better  still,  the  sun.  The  rays,  after  reflection  from  the 
silvered  surface  of  the  membrane,  are  made  parallel  by  pass- 
ing through  the  lens,  R,  and  the  position  of  the  instrument 
is  adjusted  so  that  these  rays  may  fall  upon  the  parabolic 
reflector,  CC,  of  the  receiver,  shown  in  Fig.  53.  This  mir- 
ror is  formed  of  copper,  plated  with  silver,  and  in  its  focus 
is  fixed  a selenium  cell,  S,  in  circuit  with  the  battery, 


184 


ELECTRICITY  IN  MODERN  LIFE 


P,  and  a pair  of  telephones,  TT,  which  are  placed  to  the 
ears  of  the  listener,  as  shown  in  the  illustration. 

Dr,  Chichester  BelV s Water-Jet  Telephone  Transmitter. — 
In  the  year  1886  Dr.  Chichester  A.  Bell  read  a paper  at  the 
Eoyal  Society  on  “The  Sympathetic  Vibrations  of  Jets,”  in 
which  he  gave  an  account  of  a series  of  experiments,  some 
of  which  led  to  the  invention  of  the  water-jet  trans- 
mitter. When  a jet  of  water  issues  from  a narrow 
orifice  it  gradually  becomes 
discontinuous,  breaks  up 
into  drops,  as  shown  in  Fig. 

54,  which  is  taken  from  an 
instantaneous  photograph. 

One  of  Dr.  Bell’s  early  ex- 
periments in  this  direction 
consisted  of  producing 
sounds  by  communicating 
either  mechanical  or  acous- 
tic vibrations  to  a jet  of  this 
kind.  The  apparatus  em- 
ployed is  shown  in  Fig.  55. 

It  consists  of  a membrane 
of  stretched  India  - rubber, 
forming  a cap  to  a brass 
tube  which  can  be  raised 
or  lowered  by  sliding  in  a 
larger  tube  resting  on  a heavy  stand.  The  upper  tube  has 
an  orifice  at  one  side  of  the  upper  end,  to  which  is  attached 
a vulcanite  trumpet.  When  a jet  of  water  is. allowed  to  fall 
upon  the  stretched  membrane,  either  mechanical  or  sound 
vibrations  communicated  to  the  jet  can  be  reproduced. 
The  loudness  and  distinctness  of  the  resulting  sound  both 


i 

Fig.  54. 


Fig.  55. 


THE  TELEPHONE 


185 


increase  up  to  a certain  point  as  the  distance  of  the  mem- 
brane from  the  orifice  is  increased,  but  after  passing  this 
point,  though  the  sound  continues  to  increase  in  loudness, 
it  begins  to  lose  its  distinctness,  until  ultimately  it  becomes 
a mere  unmusical  roar,  when  it  will  be  found  that  the  jet  has 
become  discontinuous  above  the  membrane.  When  the  jet 
is  carefully  adjusted  so  as  to  obtain  the  best  effects,  the 
loudness  of  the  sounds  produced  is  very  striking;  for  exam- 
ple, if  the  board  to  which  the  tube  is  attached  is  scratched 
with  the  finger,  or  if  a watch  is  held  in  contact  with  the 
tube,  the  sounds  produced  can  be  heard  distinctly  through- 
out a room  containing  several  hundred  people.  If  the  jet 
is  allowed  to  fall  upon  the  top  of  a narrow  vertical  rod,  it 
spreads  out  into  a nappe;  and  Dr.  Bell  found  that  this 
nappe  was  capable  of  responding  to  vibrations  just  like 
the  jet,  and  it  is  this  property  which  is  utilized  in  the 
construction  of  the  water-jet  transmitter.  The  principle  of 
the  instrument  consists  in  including  the  nappe  of  a jet 
of  conducting  liquid  in  a circuit  traversed  by  a current 
from  a battery,  and  containing  an  ordinary  telephone.  The 
nappe  formed  by  the  impact  of  a steady  jet  retains  a con- 
stant diameter,  but  when  thrown  into  vibration  it  undergoes 
periodic  changes  in  diameter,  and  therefore  also  in  resist- 
ance, which  Dr.  Bell  considers  to  be  due  in  part  to  the 
changes  in  diameter,  and  in  part  to  changes  in  the  contact 
resistance,  arising  from  the  motions  of  the  particles  of 
liquid,  so  that  the  current  passing  through  the  circuit  un- 
dergoes corresponding  continuous  vibrations  in  strength, 
as  in  other  forms  of  telephonic  transmitters.  The  simplest 
way  of  passing  a current  through  it  consists  in  allowing  the 
jet  to  strike  normally  upon  the  exposed  end  of  a platinum 
wire  imbedded  in  an  insulator  which  is  impervious  to,  and 


186 


ELECTRICITY  IN  MODERN  LIFE 


unaffected  by,  the  liquid  employed,  and  which  is  sur- 
rounded by  a platinum  ring  which  comes  in  contact  with 
the  outer  portions  of  the  nappe. 

The  most  suitable  liquid  consists  of  water  acidulated 
with  about  of  its  volume  of  pure  sulphuric  acid. 

The  battery  must  be  of  high  E.M.P.,  but  its  resistance 
is  of  little  consequence,  owing  to  the  high  resistance  of  the 
transmitter.  A battery  of  about  twenty  small  zinc-carbon 
cells,  charged  with  a solution  of  sal-ammoniac,  gives  very 
good  results  with  the  liquid  described,  but  the  number  of 
cells  may  be  increased  with  advantage,  not,  however,  to 
such  an  extent  as  to  electrolyze  the  liquid,  as  the  noise 
produced  in  the  receiving  telephone  by  the  escape  of  gas 
bubbles  would  drown  the  sounds  due  to  the  vibratory 
changes  in  the  jet.  The  pressure  required  increases  with 
the  size  of  the  jet,  and  with  jets  of  the  most  suitable  size 
a pressure  of  a little  under  three  feet  of  water  gives  the 
best  results. 

A simple  experimental  form  of  apparatus  is  shown  in 
Fig.  56.  The  jet  tube,  J,  is  mounted  on  the  sound-board 
S.  The  receiving  surface  is  formed  by  the  end,  E',  of  an 
ebonite  plug.  A platinum  wire,  E,  passes  water-tight  up 
the  plug,  and  its  upper  exposed  surface  forms  the  inner 
electrode  of  the  transmitter.  The  outer  electrode,  E',  con- 
sists of  a small  tube  of  platinum  foil  concentric  with  the 
upper  extremity  of  the  wire  E,  and  insulated  from  it  by 
the  ebonite.  After  it  has  been  fitted  on,  the  top  of  the 
ebonite  plug  is  turned  off,  so  as  to  present  a smooth  con- 
tinuous surface,  slightly  convex. 

Fine  platinum  wires  welded  to  E and  E'  serve  to  ^connect 
them  with  the  terminals  of  the  circuit.  C is  an  ebonite  cup 
which  supports  the  plug,  and  receives  the  waste  water  which 


THE  TELEPHONE 


187 


escapes  through  the  tube  T.  F is  a filter,  closed  by  screw 
caps,  K and  K'.  Through  the  upper  cap  pass  two  tubes, 
X and  Y,  which  are  connected  with  a reservoir  and  the  jet 
respectively,  by  means  of  black  India-rubber  tubing.  Two 
perforated  ebonite  disks  are  fitted  within  the  cylinder,  and 


the  space  between  them  is  tightly  packed  with  coarse  cot- 
ton, which  has  been  freed  from  grease  by  soaking  in  a solu- 
tion of  caustic  potash,  and  been  thoroughly  washed  with 
dilute  sulphuric  acid  and  water.  The  filter  is  necessary  to 
keep  back  particles  of  dirt  which  might  stop  the  orifice,  and 
also  air  bubbles,  the  presence  of  which  sets  up  vibrations 
and  gives  rise  to  a crackling  sound  in  the  receiving  telephone. 


188 


ELECTRICITY  IN  MODERN  LIFE 


I have  made  some  experiments  with  an  instrument  of  this 
kind,  but  with  the  jet  pressed  laterally  against  the  sound- 
board, which  was  about  a quarter  of  an  inch  thick,  and  was 

fixed  in  a vertical  position.  It 
reproduced  with  perfect  distinct- 
ness the  voice  of  a person  speak- 
ing in  the  tone  of  ordinary  con- 
versation at  a distance  of  twenty 
feet  from  the  instrument;  and 
when  standing  in  a room  with 
an  open  window,  it  reproduced 
the  sounds  of  a piano  played  in 
a room,  in  which  there  was  also 
an  open  window,  at  the  opposite 
side  of  the  street.  On  another 
occasion  I succeeded  in  obtain- 
ing an  exceptionally  clear  and 
pure  reproduction  of  the  voices 
of  four  boys  singing  in  unison  in 
a room  in  which  the  transmitter 
was  placed.  When  the  Edison 
loud-speaker  previously  referred 
to  was  used  with  this  transmitter, 
in  place  of  an  ordinary  Bell  re- 
ceiver, very  good  results  were 
also  obtained.  This  form  of  ap- 
paratus is,  however,  not  suitable 
for  practical  work,  as  in  addition 
Fig.  57.  to  its  requiring  separate  vessels 

to  act  as  reservoir,  and  to  receive  the  waste  liquid  respec- 
tively, it  requires  careful  adjustment  whenever  it  is  to  be 
used.  The  inventor  has  recently  devised  an  apparatus 


THE  TELEPHONE 


189 


(shown  in  Fig.  57)  which  combines  simplicity  and  certainty 
of  action  with  durability.  The  whole  apparatus  is  inclosed 
in  a case  of  teak  or  mahogany  about  three  feet  high,  and 
is  protected  in  front  by  a cover  which  opens  on  hinges, 
and  is  provided  with  a lock  and  key.  There  is  a round 
aperture  protected  by  crossed  copper  wires  opposite  the 
transmitting  jet,  and  in  using  the  instrument  the  mouth  of 
the  speaker  is  placed  at  a distance  of  a few  inches  from  this 
aperture,  as  it  is  neither  requisite  nor  desirable  to  have 
a jet  as  sensitive  as  that  of  the  experimental  apparatus 
previously  described. 

The  electrodes  in  this  instrument  are  formed  of  a plati- 
num wire  passing  up  the  centre  of  a glass  plug  and  a con- 
centric ring  of  fine  platinum  wire,  glass  being  used  instead 
of  ebonite  on  account  of  its  being  found  more  durable. 
The  jet  and  plug  are  contained  in  a glass  tube  attached  to 
a wooden  box,  resting  on  the  bottom  of  the  case,  which 
receives  the  waste  liquid. 

The  glass  plug  is  rigidly  fixed  in  a vertical  position,  and 
the  jet  is  centrally  adjusted  over  it  by  means  of  the  four 
screws  shown  at  the  upper  end  of  the  containing  tube.  The 
filter  is  seen  on  the  left-hand  side  of  the  jet;  its  exit  tube 
has  its  extremity  enlarged  into  a bell  which  contains  the 
cotton,  and  the  fibres  of  this  are  prevented  from  passing  into 
the  narrow  part  of  the  tube  by  means  of  a piece  of  cotton 
material  placed  at  the  top  of  the  bell.  The  reservoir  con- 
sists of  a second  box  similar  to  the  first,  placed  at  the  top 
of  the  instrument,  and  is  filled  by  taking  out  a screw  plug 
in  the  centre  of  its  upper  side,  and  pouring  the  liquid  in 
through  a funnel. 

The  terminals  of  the  receiving  telephone  are  connected 
with  the  two  left-hand  binding  screws,  the  lower  one  of 


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ELECTRICITY  IN  MODERN  LIFE 


which  is  connected  to  one  electrode  of  the  transmitter,  and 
the  upper  one  to  a pair  of  springs  which  make  contact  with 
the  lever  from  which  the  telephone  is  suspended,  when  the 
latter  is  removed  and  the  supporting  hook  is  allowed  to 
rise.  The  other  electrode  is  connected  with  the  lowermost 
of  the  binding  screws  on  the  right,  which  is  put  to  earth 
through  the  battery;  the  central  right-hand  binding  screw 
is  in  permanent  connection  through  the  call  apparatus 
with  the  line,  and  also  with  a spring  which  makes  con- 
tact with  the  telephone  lever  when  the  telephone  is  hung 
up.  To  speak  through  the  instrument  the  telephone  is 
taken  ofi,  but  the  hook  end  of  its  supporting  lever  is  pre- 
vented from  rising  by  means  of  the  vertical  lever  shown. 
The  handle  on  the  right-hand  side  of  the  case  is  now  de- 
pressed, when  a pin  on  its  lower  end  draws  back  the  vertical 
lever  and  allows  the  telephone  hook  to  rise,  placing  the 
telephone  in  circuit  with  the  line. 

The  telephone  lever  in  rising  pushes  up  a brass  rod 
hinged  to  it,  thus  lifting  the  left-hand  end  of  the  lever 
above  the  reservoir,  and  opening  a valve  which  allows  the 
fluid  in  the  reservoir  to  flow  down  an  ebonite  tube  on 
the  left-hand  side  into  the  filter.  A second  ebonite  tube 
passes  from  the  filter  and  opens  into  the  top  of  the  reservoir 
to  allow  air  to  escape  immediately,  if  the  filter  has  run 
partially  dry  from  the  instrument  remaining  unused  for 
some  time.  The  depression  of  the  right-hand  lever  at  the 
same  time  compresses  an  India-rubber  bag  shown  in  the  cen- 
tre of  the  case,  and  thereby  drives  air  into  the  lower  box 
through  an  ebonite  tube  seen  on  the  right-hand  side,  which 
is  provided  at  its  upper  end  with  a valve  opening  inward, 
and  forces  liquid  from  the  lower  reservoir,  through  the  other 
ebonite  tube  on  the  right  hand,  into  the  upper  reservoir. 


THE'  TELEPHONE 


191 


The  amount  of  liquid  pumped  up  by  one  depression  of 
the  lever  is  sufficient  for  about  seven  minutes’  conversation, 
and  as  the  average  length  of  a conversation  would  usually 
be  less  than  this,  there  will  be  enough  liquid  in  the  upper 
reservoir  to  allow  of  a longer  conversation  as  often  as  it  is 
likely  to  be  wanted,  without  pumping  up  fresh  fluid,  which, 
however,  does  not  interfere  in  any  way  with  the  conversa- 
tion being  carried  on.  The  object  of  the  control  lever, 
which  keeps  the  telephone  out  of  circuit  until  the  right- 
hand  lever  is  depressed,  is  to  prevent  users  from  forgetting 
to  pump  up  a fresh  supply  each  time. 

The  instrument  is  chiefly  valuable  for  use  on  trunk  lines 
over  long  distances,  as  any  leakage  on  the  line  can  be  com- 
pensated by  using  additional  battery  power,  and  very  good 
results  have  been  obtained  with  it  on  lines  upward  of  a 
hundred  miles  in  length,  and  passing  through  six  or  eight 
exchanges,  and  therefore  subject  to  a considerable  amount 
of  leakage. 

The  Phonograph. — The  phonograph  is  not  an  electrical 
instrument,  and  therefore  some  apology  is  needed  for  giving 
a description  of  it  in  a volume  devoted  to  the  practical 
applications  of  electricity.  Historically,  however,  it  is  very 
closely  related  to  the  telephone,  as  it  was  Mr.  Edison’s 
telephonic  investigations  which  led  up  to  the  invention  of 
this  instrument. 

Graham  Bell,  by  his  invention  of  the  speaking  tele- 
phone, had  made  it  possible  for  conversations  to  be  carried 
on  irrespective  of  the  distance  separating  the  speakers. 
Mr.  Edison  supplemented  this  by  his  invention  of  an  in- 
strument which  in  its  present  form  enables  spoken  words 
and  other  sounds  to  be  permanently  recorded  and  repro- 
duced at  will  at  any  future  time.  Some  more  or  less  suc- 

SCIENCE — VOL.  XIII — 9 


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ELECTRICITY  IN  MODERN  LIFE 


cessful  attempts  have,  moreover,  been  made  by  Mr.  Edison 
to  combine  the  phonograph  with  the  telephone,  so  as  to 
enable  messages  sent  through  the  telephone  to  be  recorded 
at  the  receiving  station  in  the  absence  of  .a  listener,  and 
repeated  by  the  phonograph  at  any  convenient  time. 

These  considerations,  -combined  with  the  great  interest 
attaching  to  the  invention,  will,  I trust,  be  considered  as 
affording  sufficient  ground  for  what  at  first  sight  might 


Fig.  58. 


seem  like  a somewhat  arbitrary  deviation  from  the  plan  of 
the  present  volume. 

The  original  form  of  the  instrument,  as  designed  in  the 
year  1877,  is  shown  in  Fig.  68.  It  consisted  of  a brass 
cylinder  upon  which  a spiral  groove  was  cut,  mounted  upon 
a screw-threaded  axis,  and  capable  of  being  made  to  rotate, 
and  at  the  same  time  move  onward  in  the  direction  of  its 
length,  by  means  of  a handle.  A heavy  fly-wheel  attached 
to  the  end  of  the  shaft  opposite  to  the  handle  enabled  an 
approximately  uniform  rate  of  rotation  to  be  maintained. 

A sheet  of  tin-foil  was  wrapped  round  the  brass  cylinder, 
and  on  this  rested  a metallic  point  attached  to  a metal 
diaphragm  stretched  underneath  a mouthpiece,  as  shown 
in  the  illustration.  When  the  mouthpiece  was  spoken  into, 


THE  TELEPHONE 


193 


the  diaphragm  was  set  in  vibration,  causing  the  latter  to 
vibrate  up  and  down  against  the  tin-foil  just  above  the 
helical  groove-cut  in  the  cylinder,  and  make  a series  of 
indentations  of  varying  depth  in  the  foil.  The  reproducing 
arrangement  consisted  simply  of  a second  diaphragm,  held 
in  a tube  on  the  opposite  side  of  the  brass  cylinder,  and 
a metal  point  which  was  held  against  the  tin-foil  by  means 
of  a delicate  spring.  This  mouthpiece  could  be  placed  in 
contact  with  the  cylinder,  or  lifted  off  it,  by  means  of  a 
lever  working  upon  a pivot,  and  when  it  was  desired  to 
reproduce  speech  or  other  sounds  from  the  tin-foil  record, 
this  mouthpiece  was  simply  placed  against  the  cylinder, 
the  trumpet  shown  at  the  right-hand  side  of  the  illustration 
being  attached  to  the  end  of  the  tube  to  increase  the  loud- 
ness of  the  sound,  and  the  cylinder  was  made  to  rotate  in 
the  same  direction,  and  as  nearly  as  possible  at  the  same 
speed  as  while  the  record  was  being  made.  Much  more 
satisfactory  results  were  obtained  from  this  instrument 
when  the  handle  for  turning  the  brass  cylinder  was  replaced 
by  means  of  clock-work,  and  a very  beautiful  instrument 
of  this  kind  was  made  by  Mr.  Stroh;  and  was  exhibited, 
together  with  an  instrument  of  the  original  type,  by  Mr. 
Preece,  at  a lecture  delivered  before  the  Physical  Society 
of  London  in  March,  1878.  This  was  the  first  public  exhi- 
bition of  the  new  invention  in  this  country,  and  it  excited 
the  greatest  interest,  the  lecture-room  of  the  Society  being 
crowded  with  members  and  their  friends. 

The  meeting  itself  was  perhaps  the  most  uproarious 
meeting  of  a learned  society  on  record;  the  mechanical  re- 
production, in  a very  “tinny”  voice,  of  such  familiar  rhymes 
as  “Old  mother  Hubbard  went  to  the  cupboard,”  and  “We 
don’t  want  to  fight,  but  by  Jingo  if  we  do,”  the  latter  of 


194 


ELECTRICITY  IN  MODERN  LIFE 


which  was  then  a favorite  music-hall  ditty,  exciting  roars 
of  laughter  among  the  audience.  Considerable  amusement 
was  excited  by  a gentleman  who  attempted  to  sing  the 
words  of  “Auld  Lang  Syne”  into  the  instrument.  After 
completing  the  line  “Should  auld  acquaintance  be  forgot,” 
he  found  that  he  was  singing  too  high,  and  he  called  out 
to  Mr.  Stroh,  who  was  superintending  the  instrument,  “Stop 
a minute;  I will  go  on  in  a lower  key!”  This  he  proceeded 
to  do,  but  as  he  had  forgotten  to  take  his  mouth  away  from 
the  instrument  while  making  his  sudden  ejaculation,  the 
instrument,  in  reproducing  the  song,  stopped,  and  repeated 
the  observation  in  exactly  the  same  hurried  tone  in  which 
it  was  originally  made,  after  which  it  sang  the  rest  of  the 
song  in  the  proper  key. 

Edison’s  original  instrument,  however,  was  nothing  more 
than  a toy,  for  in  the  first  place  it  required  very  careful 
adjustment;  and  several  attempts  often  had  to  be  made, 
with  a fresh  piece  of  tin-foil  each  time,  before  the  machine 
could  be  got  to  speak;  and  in  the  second  place,  after  the 
sounds  had  been  reproduced  two  or  three  times,  the  record 
became  worn  out;  while,  lastly,  it  was  impossible  to  remove 
the  tin-foil  from  the  cylinder  and  replace  it  without  injury. 

Edison  made  a great  many  attempts  to  remedy  these 
defects,  and  among  others  he  tried  the  effect  of  using  a wax 
cylinder  with  tin-foil  stretched  over  it,  and  actually  took 
out  a patent  for  this  arrangement.  His  attempts,  however, 
were  unsuccessful,  and  ultimately  he  laid  the  instrument 
aside,  for  reasons  which  it  may  be  as  well  to  give  in  his 
own  words,  quoted  from  an  interview  published  in  the 
“Electrical  World” — a New  York  paper — on  November 
12,  1887.  Speaking  of  the  phonograph,  Mr.  Edison  said — 
“It  weighs  about  one  hundred  pounds;  it  costs  a mint  of 


THE  TELEPHONE 


195 


money  to  make;  no  one  but  an  expert  could  get  anything 
back  from  it;  the  record  made  by  the  little  steel  point  upon 
a sheet  of  tin-foil  lasted  only  a few  times  after  it  had  been 
put  through  the  phonograph.  I myself  doubted  whether 
I should  ever  see  a perfect  phonograph  ready  to  record  any 
kind  of  ordinary  speech,  and  to  give  it  out  again  intelli- 
gibly. But  I was  perfectly  sure  if  we  did  not  accomplish 
this,  the  next  generation  would.  And  I dropped  the 
phonograph,  and  went  to  work  upon  the  electric  light, 
certain  that  I had  sown  seed  which  would  come  to  some- 
thing.” Mr.  Edison’s  expectations  were  realized  sooner 
than  he  anticipated.  In  the  spring  of  1881  an  arrangement 
was  made  between  Alexander  Graham  Bell,  the  inventor  of 
the  telephone.  Dr.  Chichester  Bell,  and  Charles  Sumner 
Tainter,  resulting  in  the  formation  of  the  Yolta  Laboratory 
Association;  this  name  being  given  to  it  because  the  capital 
with  which  the  first  start  was  made  was  provided  by  the 
Yolta  prize  of  50,000  francs,  which  had  been  awarded  to 
Graham  Bell  by  the  French  Government  for  his  invention 
of  the  telephone.  The  object  of  this  partnership  was  stated 
to  be  “the  study  and  elaboration  of  ideas,  inventions,  and 
discoveries  relating  to  the  art  of  transmitting,  recording, 
and  reproducing  sounds.” 

The  actual  work  was  mainly  done  by  Dr.  Chichester 
Bell,  a trained  physicist,  and  Mr.  Tainter,  an  exceedingly 
skilful  and  ingenious  mechanic.  The  first  part  of  their 
work  consisted  in  studying  the  causes  of  failure  in  the 
phonograph,  and  they  soon  came  to  the  conclusion  that 
tin-foil  or  any  other  pliable  substance  was  unsuitable,  and 
that  the  record  should  be  produced  on  a plate  of  some  solid 
material;  and  also  that  a satisfactory  reproduction  could  not 
be  obtained  by  any  process  of  indentation,  but  that  a cutting 


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ELECTRICITY  IN  MODERN  LIFE 


style  must  be  used,  adapted  to  grave  or  gouge  out  the 
material  acted  upon,  in  a groove,  the  bottom  of  which 
would  thus  be  made  to  form  a continuous  wavy  curve. 
This  substitution  of  a continuous  curve  for  the  separate 
indentations  of  Edison’s  instrument  was  as  great  an  im- 
provement upon  the  original  phonograph  as  that  which 
Graham  Bell  had  effected  in  the  telephone  by  substituting 
a continuous  undulatory  current  for  the  series  of  intermit- 
tent currents  produced  by  making  and  breaking  contact  in 
Eeis’s  telephone. 

After  trying  a large  number  of  substances,  a kind  of 
wax  containing  a considerable  proportion  of  paraffin  was 
found  most  suitable,  and  after  some  years  of  continuous 
work  a phonograph  was  produced,  capable  of  reproducing 
sounds  with  great  clearness,  and  apparently  an  unlimited 
number  of  times,  the  same  wax  cylinder  having  been  made 
to  repeat  the  words  engraved  upon  it  more  than  a thousand 
times  without  showing  any  signs  of  deterioration. 

The  instrument  was  called  the  Graphophone  or  Grapho- 
phone-Phonograph,  in  order  to  distinguish  it  from  Edison’s 
original  instrument.  It  was  completed  in  the  year  1885, 
and  was  exhibited  privately  to  one  of  Edison’s  associates 
at  Washington,  and  also  to  some  members  of  the  Edison 
Phonograph  Company,  which  had  been  formed  soon  after 
the  invention  of  the  original  instrument,  and  when  it  was 
still  hoped  that  it  might  be  made  a practical  success.  The 
instrument  was  patented  in  the  following  year. 

Its  present  form  is  shown  in  Pig.  59,  which  exhibits  an 
operator  speaking  into  the  instrument,  while  Pig.  60  shows 
the  operator  receiving  a message,  and  writing  it  down  on  a 
typewriter.  The  cylinders  are  made  of  paper  covered  with 
a thin  layer  of  wax,  and  are  held  in  position  in  the  machine 


Fkj.  51) 


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197 


by  being  gripped  between  conical  projections  on  a pair  of 
pulleys  turning  about  axes  in  the  same  straight  line.  The 
cylinder  is  made  to  rotate  by  means  of  a driving-wheel 
worked  by  a treadle,  and  controlled  by  a governor  of  exceed- 
ingly ingenious  construction,  the  invention  of  Mr.  Tainter. 
This  governor  is  so  constructed  that,  as  long  as  the  speed 


Fig.  60. 


of  the  driving-wheel  exceeds  a certain  minimum^  the 
speed  of  the  cylinder  is  maintained  almost  absolutely  con- 
stant. The  cylinder  is  not  made  to  move  forward  as  in  the 
original  phonograph,  but,  instead  of  this,  the  cutting  style 
with  its  diaphragm,  or  the  recorder,  as  the  case  may  be,  is 
made  to  move  along  an  axle  with  a screw-thread  cut  in  it, 
which  rotates  parallel  to  the  axis  of  the  cylinder.  While 


198 


ELECTRICITY  IN  MODERN  LIFE 


the  machine  is  running,  the  motion  of  the  cylinder  and 
style  can  be  started  or  stopped  instantaneously  by  simply 
pressing  a button,  which  is  a great  convenience  both  in 
dictating  to  the  machine  and  in  writing  down  from  its  dicta- 
tion. In  speaking  to  the  instrument  the  operator  is  thus 
able,  at  the  end  of  a sentence,  to  stop  the  motion  of  the 
cylinder,  and  so  prevent  any  waste  of  space  while  he  is 
thinking  over  the  composition  of  his  next  sentence;  and 
again,  a clerk  writing  from  the  dictation  of  the  instrument 
can  take  off  as  few  words  as  he  likes  at  a time,  so  that  he 
can  write  down  the  record  without  any  difficulty,  either 
with  a pen  or  upon  a typewriter.  Some  of  the  instruments 
first  made  were  constructed  so  as  to  speak  loudly  enough 
to  be  heard  by  a number  of  persons  together  without  the 
assistance  of  a hearing  tube. 

This  was  effected  by  cutting  the  screw-thread  of  the  axle 
which  drives  the  recorder  and  transmitter  rather  coarsely, 
so  as  to  leave  a comparatively  wide  space  between  the 
different  portions  of  the  helix  forming  the  record. 

In  all  the  instruments  which  have  hitherto  been  imported 
into  this  country,  however,  the  thread  is  cut  much  finer, 
with  the  object  of  enabling  as  many  words  as  possible  to  be 
put  on  each  cylinder,  and  thereby  minimizing  the  number 
of  cylinders  required.  This  necessitates  the  use  of  hearing 
tubes,  as  shown  in  the  illustration,  Fig.  60.  For  practical 
use  this  does  not  cause  any  inconvenience.  One  of  the 
great  advantages  of  the  graphophone  for  practical  purposes 
is  that,  when  the  machines  have  been  properly  adjusted  at 
the  factory,  no  further  adjustment  is  required  in  using 
them,  and  the  cylinders  can  be  put  in  or  taken  out  in  a 
moment. 

Within  the  last  year  or  two  Mr.  Edison  has  again  turned 


Science^  /.  199 — Vol.  13 


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his  attention  to  the  improvement  of  the  phonograph,  and 
some  very  beautiful  instruments  which  he  has  recently 
constructed  have  been  sent  over  to  this  country  and  ex- 
hibited by  Colonel  Grourand.  One  of  these  is  shown  in 
Fig.  61.  In  these  instruments  he  makes  use  of  cylinders 
of  considerable  size  made  out  of  solid  wax,  and  the  instru- 
ment is  provided  with  an  arrangement  for  shaving  off  the 
surface  of  the  cylinder  before  a record  is  made  upon  it, 
which  produces  an  exceedingly  true  surface,  and  greatly 
improves  the  clearness  with  which  speech  and  music  can 
be  reproduced,  as  it  almost  entirely  obviates  the  slight 
scratching  sound  generally  heard  in  the  graphophone,  owing 
to  small  inequalities  in  the  surface  of  the  wax.  Mr.  Edison’s 
instrumeuts  are  mostly  driven  by  small  electro-motors  ener- 
gized by  means  of  one  or  two  bichromate  or  other  conven- 
ient cells,  and  controlled  by  a centrifugal  governor  similar, 
on  a miniature  scale,  to  those  which  are  employed  on  steam 
engines.  This  mode  of  driving  the  machinery  has  the  ad- 
vantage of  making  the  speed  extremely  uniform,  with  the 
result  of  still  further  improving  the  quality  of  the  reproduc- 
tion. It  is,  however,  not  altogether  satisfactory  for  general 
use,  as  primary  batteries  are  troublesome  things  to  keep  in 
order,  except  in  the  hands  of  those  who  have  some  practical 
knowledge  of  electricity. 

Another  defect,  which  will  have  to  be  overcome  before 
Edison’s  new  phonograph  can  be  considered  a really  prac- 
tical instrument  for  everyday  use,  is  that  whenever  a new 
cylinder  is  placed  upon  it,  it  requires  careful  adjustment, 
and  will  therefore  not  give  satisfactory  results  except  in 
skilled  hands. 


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ELECTRICITY  IN  MODERN  LIFE 


CHAPTER  XIII 

THE  TELEPHONE  EXCHANGE  SYSTEM 

WHEN  the  telephone  was  first  introduced  into  this 
country  it  was  almost  universally  regarded  by 
scientific  men,  both  in  England  and  America,  as 
little  more  than  a scientific  toy,  though  a very  beautiful  and 
interesting  one;  and  although  it  was  soon  discovered  that 
it  would  prove  an  instrument  of  great  value  for  the  purpose 
of  electrical  research,  it  might  long  have  remained  a mere 
laboratory  instrument,  had  it  not  been  for  the  practical 
acumen  of  Mr.  Graham  Bell’s  father-in-law,  Mr.  Hubbard, 
who  soon  foresaw  that  the  instrument  might  be  turned  to 
practical  account;  this  was  effected  by  the  development 
of  the  telephone  exchange  system,  in  which  Mr.  Hubbard 
played  a very  important  part. 

Telephone  exchanges  were  first  introduced  in  America, 
where  they  soon  proved  a commercial  success;  from  there 
they  spread  into  other  countries,  and  before  long  their  use 
became  so  general  that  at  present  business  men  would  hardly 
know  how  to  do  without  them. 

The  simplest  way  of  explaining  in  a short  compass  the 
principles  of  the  telephone  exchange  system  will  be  to  give 
an  account  of  the  actual  exchanges  in  some  one  place,  and 
I shall  select  the  London  system  of  exchanges  for  that 
purpose. 


Fig.  62— Plan  of  London  Telephone  Exchange 


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Fig.  62  is  a plan  of  the  exchange  system  existing  in 
London  at  the  beginning  of  1888.  The  exchanges  are  de- 
noted by  circles,  which  are  placed  so  as  to  make  the  diagram 
as  simple  a one  as  possible,  and  not  in  their  relative  geo- 
graphical positions. 

Bach  of  the  exchanges  is  connected  by  one  or  more 
trunk  wires,  as  they  are  called,  shown  by  dotted  lines  in 
the  diagram,  with  the  central  exchange  at  Oxford  Court, 
Cannon  Street.  The  continuous  lines  show  the  wires  con- 
necting the  local  exchanges,  and  the  small  figures  attached 
to  these  lines  show  the  number  of  wires  between  each  pair 
of  exchanges.  There  are  at  present  about  five  thousand 
subscribers  in  connection  with  this  system  of  exchanges, 
including  the  subscribers  at  Brighton,  which  is  in  connec- 
tion with  the  London  system. 

Every  subscriber  has  a telephone  fixed  in  his  own  house 
or  office,  and  when  he  wishes  to  speak  to  another  subscriber 
he  goes  up  to  his  telephone  and  makes  a call  signal.  This 
is  transmitted  to  the  local  exchange  with  which  he  is  con- 
nected, and  one  of  the  clerks  at  the  exchange  immediately 
replies  to  him.  He  then  states  the  number  of  the  subscriber 
with  whom  he  wishes  to  speak,  each  subscriber  having  a 
certain  number  assigned  to  him.  If  the  subscriber  with 
whom  he  wishes  to  communicate  is  on  the  same  local  ex- 
change, the  clerk  at  once  makes  the  required  connection, 
provided  the  wire  of  the  latter  is  disengaged — that  is  to  say, 
if  the  latter  subscriber  is  not  actually  using  his  telephone  in 
speaking  to  some  one  else.  If  the  second  subscriber  is  on 
a different  local  exchange,  the  clerk,  if  there  is  a direct 
wire  connecting  the  two  exchanges,  signals  his  number 
to  the  second  exchange,  and  then  the  clerks  at  the  two 
exchanges  connect  the  telephone  wires  from  the  houses  of 


202 


ELECTRICITY  IN  MODERN  LIFE 


the  two  subscribers,  through  the  wire  joining  the  two  ex- 
changes. If,  on  the  other  hand,  there  is  no  wire  directly 
connecting  the  two  exchanges,  the  clerk  at  the  first  ex- 
change calls  the  central  exchange  at  Oxford  Court,  and 

indicates  the  subscriber  with  whom 
communication  is  to  be  established. 
The  clerk  at  the  central  exchange  then 
passes  on  the  number  to  the  proper 
local  exchange,  and  the  clerk  there 
sends  a call  signal  to  the  subscriber, 
and  then  connects  him  - to  the  trunk 
wire  at  Oxford  Court,  so  that  the  two 
subscribers  are  placed  in  communica- 
tion through  the  central  exchange. 

The  manner  in  which  these  opera- 
tions are  carried  out  is  fairly  simple 
and  easily  understood.  The  set  of  tele- 
phone apparatus  with  which  each  sub- 
scriber is  supplied  consists  of  a carbon 
transmitter  of  the  Blake  pattern,  a Bell 
receiver,  a battery,  and  a small  mag- 
neto-machine worked  by  a handle,  for 
making  the  call  signals. 

The  telephone  is  suspended  from  a 
hook  similar  to  that  used  in  the  water- 
jet  transmitter,  described  in  Chapter 
XII.  While  the  telephone  is  on  its 
hook  the  subscriber  turns  the  handle 
of  the  magneto  to  call  the  exchange;  he  then  takes  the 
telephone  ofi  the  hook,  thereby  throwing  the  magneto  out 
of  circuit,  and  connects  his  receiver  with  the  line  as  then 
described,  except  that  the  connection  with  the  line  is  made 


■fa 


library 

OF  THE 


THE  TELEPHONE  EXCHANGE  SYSTEM 


203 


directly  when  the  hook  rises,  instead  of  by  the  subsequent 
motion  of  a lever. 

The  exchange  is  provided  with  an  instrument  called 
a switch-board,  and  it  will  be  easier  to  understand  the 
process  followed  by  considering  in  the  first  place  a switch- 
board of  a somewhat  simpler  construction  than  those  usually 
employed  in  the  London  exchanges. 

Fig.  63  shows  a simple  form  of  switch- 
board adapted  for  fifty  subscribers. 

W hen  the  person  who  wishes  to  call 
the  exchange  turns  the  handle  of  his 
magneto,  a current  is  sent  through  the 
line  and  the  coils  of  a small  electro- 
magnet placed  at  the  back  of  the  upper 
part  of  the  board,  immediately  behind 
one  of  the  drop-shutters  shown  in  the 
illustration.  The  electro-magnet,  being 
excited  by  this  current,  lifts  a small 
catch,  which  allows  the  shutter  to  drop, 
disclosing  the  number  of  the  sub- 
scriber. The  clerk  at  the  exchange 
then  presses  a plug  connected  with  his 
own  transmitter  and  receiver  into  one  of 
the  holes,  shown  in  the  lower  portion 
of  the  board,  marked  with  the  same 
number  as  the  one  disclosed  by  the  fall 
of  the  shutter.  This  connects  the  operator  by  means  of 
what  is  called  a “spring- jack,”  shown  in  Fig.  64,  placed 
at  the  back  of  the  board,  with  the  calling  subscriber. 

The  contact  plug  passes  through  the  collar  shown  in  the 
lower  part  of  the  illustration,  and  makes  contact  with 
the  left-hand  spring,  at  the  same  time  lifting  it  off  the  con- 


Fia.  64. 


204 


ELECTRICITY  IN  MODERN  LIFE 


tact  button  shown,  and  thereby  breaking  its  connection 
with  the  right-hand  spring.  The  left-hand  spring  is  insu- 
lated, and  in  connection  with  the  calling  subscriber’s  wire, 
while  the  right-hand  spring  is  earth-connected.  When  the 
operator  has  introduced  his  plug,  he  replies  to  the  calling 
subscriber  by  means  of  his  transmitter,  and  then  listens  at 
his  receiver  until  the  subscriber  who  called  has  stated 
the  number  of  the  subscriber  with  whom  he  wishes  to 
communicate. 

When  this  has  been  done  the  operator  inserts  his  plug 
into  the  opening  of  the  spring-jack  corresponding  to  the 
subscriber  who  is  to  be  called,  and  presses  a key,  which 
sends  a current  into  the  line,  from  a battery  or  other  gen- 
erator at  the  station,  and  rings  the  latter  subscriber’s  bell. 
The  operator  then  removes  his  own  plug  and  places  the  two 
subscribers  in  connection  by  taking  up  a pair  of  plugs 
connected  by  means  of  a flexible  wire  cord,  as  shown  in 
the  illustration.  They  can  then  carry  on  conversation 
as  long  as  they  wish,  and  when  they  have  finished  each 
subscriber  turns  the  handle  of  his  magneto,  and  the  current 
from  this  causes  one  of  the  clearing-out  drops  at  the  bottom 
of  the  board  to  fall,  indicating  to  the  clerk  at  the  exchange 
that  his  line  may  be  cleared.  Subscribers  often  forget  to 
give  the  clearing-out  signal  when  they  have  finished  their 
conversation,  and  an  automatic  arrangement  is  therefore 
sometimes  adopted,  which  sends  a clearing-out  signal  as 
soon  as  the  subscriber  has  replaced  his  telephone  upon 
its  hook. 

If  a number  of  switchboards,  such  as  that  shown  in  Fig. 
63,  were  used  in  an  exchange  in  connection  with  a large 
number  of  subscribers,  arrangements  would  have  to  be  made 
for  making  connections  across  from  one  board  to  the  other, 


THE  TELEPHONE  EXCHANGt!  SYSTEM 


206 


and  an  operator  on  one  side  of  the  room  would  fre- 
quently have  to  shout  across  the  room  to  one  on  the 
opposite  side  in  order  to  tell  him  to  make  the  required 
connection.  An  arrangement  of  a similar  character  was 
actually  employed  in  the  earlier  exchanges.  The  method, 
however,  is  very  inconvenient,  owing  to  the  confusion 
caused  by  operators  calling  to  each  other  from  all  parts 
of  the  room,  and  the  multiple  switchboard,  a compara- 
tively recent  invention,  is  now  gradually  displacing  all 
such  systems. 

The  general  arrangement  of  a multiple  switchboard 
is  shown  in  Fig.  65,  which  illustrates  the  multiple  board 
at  the  Manchester  Exchange,  and  shows  the  operators  at 
work.  Each  operator  has  to  attend  to  a group  of  as  many 
subscribers  as  she  can  conveniently  serve,  and  the  drop- 
shutters  and  annunciators  belonging  to  these  groups  of 
subscribers  are  seen  on  the  lower  section  of  the  board. 
Each  subscriber  to  the  exchange  is  connected  to  a group  of 
spring-jacks  placed  on  the  upper  section  of  the  board,  and 
distributed  in  such  a manner  that  one  of  them  can  be  reached 
by  every  operator  without  moving  from  her  place.  The 
plugs  for  making  the  connection,  and  the  flexible  conduc- 
tors connecting  them,  are  the  same  as  those  already  de- 
scribed, but  the  spring-jacks  are  slightly  modified,  being 
constructed  and  connected  up  in  such  a manner  that  the 
line  coming  from  a subscriber  passes  behind  the  board  and 
through  all  the  spring-jacks  of  the  same  number  without 
touching  their  metallic  framework,  and  finally  goes  from 
the  electro-magnet  of  the  annunciator  to  earth.  When  a 
plug  is  introduced  into  one  of  the  switch-holes,  for  instance, 
that  of  the  middle  section  of  the  board,  the  line  passes 
directly  to  the  plug  and  its  flexible  cord.  To  explain  how 


206  ELECTRICITY  IN  MODERN  LIFE 

connection  is  made  between  the  subscribers,  suppose  that 
No.  26  has  called  the  exchange. 

The  shutter  of  his  annunciator  then  falls,  exposing  the 
number,  25,  and  the  operator  takes  a pair  of  plugs  attached 
to  one  of  the  flexible  cords,  and  inserts  one  of  them  into  the 
spring- jack  No.  25,  at  the  same  time  depressing  a key  at 
the  bottom  of  the  board,  which  places  her  own  set  of  tele- 
phone apparatus  in  circuit  with  the  telephone  wire  of  the 
calling  subscriber.  She  then  inquires  what  number  he 
wishes  to  speak  to,  and  I will  suppose  that  No.  25  informs 
her  that  he  wishes  to  speak  with  No.  875.  The  clerk  then 
touches  the  spring-jack  No.  875  with  the  plug  attached 
to  the  further  end  of  the  flexible  cord,  one  end  of  which  is 
already  in  connection  with  No.  25.  If  the  line  is  engaged 
she  will  then  hear  a noise  in  her  telephone,  but  if  no  noise 
is  heard  she  knows  that  the  line  is  free,  and  she  then  inserts 
the  plug  and  presses  a second  key,  sending  a current  from 
a generator  at  the  exchange  to  No.  875,  thereby  ringing  his 
bell.  She  then  lifts  her  hand  from  the  call  key,  and  the  two 
subscribers  are  in  communication.  When  the  conversation 
is  finished  the  subscribers  turn  the  handles  of  their  magneto 
call  bells,  causing  the  clearing-out  drops  to  fall,  and  the 
operator  then  removes  the  plugs,  which  fall  back,  owing  to 
the  counterpoise  attached  to  them,  to  their  original  position. 

In  this  country  the  use  of  the  telephone  is  almost  entirely 
confined  to  business  men,  and  to  them  it  is  of  the  utmost 
possible  value,  owing  to  the  rapidity  with  whieh  communica- 
tions can  be  made  and  replied  to.  In  all  the  large  American 
towns,  however,  it  is  extensively  employed  in  private 
houses;  and,  as  all  the  principal  shops  are  on  the  exchange, 
the  mistress  of  a house  can  sit  down  to  the  telephone  and 
order  whatever  she  may  require  during  the  day. 


207 


THE  TELEPHONE  EXCHANGE  SYSTEM 

The  houses  or  offices  of  the  professional  men,  and  the 
cab-stands,  are  also  in  connection  with  the  exchange,  so 
that,  for  example,  if  a doctor  is  wanted  in  a hurry  he  can 
be  called  in  a moment  by  telephone,  and  on  receiving 
the  message  he  can  at  once  call  for  a cab,  which  he  will 
find  waiting  at  the  door  almost  as  soon  as  he  is  ready  to 
start.  Fire  and  police  stations  are  also  in  connection  with 
the  exchange,  so  that  if  a fire  breaks  out  in  the  house,  or 
if  burglars  break  in  during  the  night,  assistance  can  be 
obtained  at  once. 

I will  conclude  this  chapter  by  an  instance,  which  came 
within  my  own  personal  knowledge,  of  the  value  of  the  tele- 
phone for  such  purposes.  A banker  at  a town  in  the  United 
States  was  one  night  absent  from  home,  and  his  wife  was 
left  with  only  women  servants  in  the  house.  After  she  had 
retired  to  rest  she  heard  some  noise  proceeding  from  the 
lower  part  of  the  house,  which  led  her  to  believe  that 
burglars  had  obtained  an  entrance.  She  at  once  got  out 
of  bed  as  quietly  as  possible,  went  into  her  dressing-room, 
where  a telephone  was  placed,  called  the  police  and  asked 
for  assistance.  In  the  course  of  a very  few  minutes  a party 
of  policemen  arri  ved  and  captured  three  negroes  who  were 
engaged  in  robbing  the  house. 


208 


ELECTRICITY  IN  MODERN  LIFE 


CHAPTER  XIV 

DISTRIBUTION  AND  STORAGE  OF  ELECTRICAL  ENERGY 

The  great  extent  to  which  electricity  is  now  being 
employed  for  lighting  purposes,  and  also  for  driv- 
ing machinery,  makes  the  question  as  to  the  most 
efficient  and  economical  means  of  distributing  and  storing 
electrical  energy  one  of  great  and  increasing  importance. 

When  the  electric  current  has  to  be  carried  to  any  con- 
siderable distance,  the  electrical  energy  can  be  transmitted 
with  greater  economy,  the  higher  the  electro-motive  force 
of  the  current.  The  reason  of  this  is  that  the  amount  of 
energy  which  can  be  obtained  from  a current  does  not 
depend  merely  on  the  strength  of  the  current,  but  is  pro- 
portional to  the  strength  of  the  current  multiplied  by  the 
electro-motive  force  by  which  it  is  driven  through  the  con- 
ductor. The  case  is  very  similar  to  that  of  distributing 
water  for  the  purpose  of  driving  machinery  by  means  of 
turbines,  the  amount  of  work  that  can  be  obtained  by  pass- 
ing a given  volume  of  water  through  a turbine  increasing 
with  the  pressure  at  which  the  water  is  supplied. 

Now  it  has  been  pointed  out  in  an  earlier  chapter  that 
when  an  electric  current  traverses  a conductor  a certain 
amount  of  its  energy  is  wasted  in  the  form  of  heat,  and  the 
quantity  of  heat  developed  being  proportional  to  the  square 


ELECTRICAL  ENERGY 


209 


of  the  current  strength  and  to  the  resistance  offered  by  the 
conductor,  it  follows  that  with  a high  electro-motive  force 
a smaller  current  will  be  required  to  supply  a given  amount 
of  energy  than  when  the  electro-motive  force  is  low,  and 
therefore  smaller  wires  can  be  used  for  conveying  it  without 
leading  to  an  undue  production  of  heat. 

In  the  case  of  currents  supplied  from  central  stations  for 
electric  lighting  and  other  purposes,  the  electro-motive  force, 
•or  electric  pressure,  developed  by  the  dynamos  is  usually 
about  two  thousand  volts.  Currents  at  this  pressure  can  be 
employed  directly  for  supplying  energy  to  a number  of  arc 
lamps,  connected  in  series,  for  lighting  open  spaces  or  large 
public  buildings,  where  the  lamps  do  not  have  to  be  lighted 
up  or  put  out  one  at  a time.  It  would  not  do,  however,  to 
introduce  a current  of  this  pressure  into  a private  house,  for 
in  the  first  place  it  would  be  exceedingly  dangerous  to  life, 
and  is  therefore  forbidden  by  law;  and  even  if  it  were 
allowable,  it  would  only  be  possible  to  use  it  for  incan- 
descent lighting,  by  joining  a very  large  number  of  lamps 
in  series,  and  starting  or  putting  them  all  out  at  the  same 
time. 

Some  method  must  therefore  be  adopted  of  transforming 
the  current  down  to  a much  lower  pressure.  If  the  current 
is  only  to  be  used  for  electric  lighting,  it  may  be  supplied 
directly  to  the  houses  from  alternating  dynamos  at  the  cen- 
tral station,  and  transformed  down  to  a low  pressure,  gen- 
erally about  one  hundred  volts,  on  entering  the  house,  by 
means  of  a piece  of  apparatus  known  as  a transformer. 
This  instrument  is  very  similar  in  its  general  character 
to  the  induction  coils  described  in  a previous  chapter. 

It  will  be  remembered  that  an  ordinary  induction  coil 
consists  of  a short  thick  coil  of  copper  wire,  wound  round 


210 


ELECTRICITY  IN  MODERN  LIFE 


an  iron  core,  and  carrying  a current  of  low  electro-motive 
force.  This  current  is  made  intermittent  by  means  of  a 
contact  breaker,  and  at  make  and  break,  secondary  cur- 
rents are  induced  by  it  in  a very  much . longer  coil  of  fine 
wire  wound  outside  the  primary  coil.  By  means  of  such 
an  instrument  a current  of  low  electro-motive  force  is  made 
to  give  rise  to  one  of  much  smaller  strength,  but  of  corre- 
spondingly higher  electro-motive  force.  A transformer  may 
be  considered  as  practically  an  induction  coil  in  which  the. 
primary  and  secondary  currents  are  interchanged,  and  the 
contact  breaker  is  done  away  with,  since  the  current  is  an 
alternating  one  as  it  comes  from  the  dynamo. 

In  this  system  the  circuit  containing  the  lamps  in  a 
house  is  complete  in  itself,  and  has  not  any  direct  con- 
nection with  the  dynamo  circuit.  The  currents  which 
energize  the  lamps  are  secondary  currents  of  low  electro- 
motive force,  but  of  considerable  strength,  produced  by  a 
primary  current  of  much  higher  electro-motive  force  and 
lower  strength.  The  transformer  is  fixed  in  any  convenient 
place  in  the  house,  being  inclosed  in  an  iron  case  and  kept 
under  lock  and  key,  so  that  the  dangerous  currents  are 
inaccessible  to  the  inmates  of  the  house. 

Another  method  of  distributing  the  current  is  by  means 
of  secondary  batteries.  It  has  already  been  pointed  out  that 
no  primary  battery  has  yet  been  discovered  capable  of  sup- 
plying electric  current  economically  upon  a large  scale;  but 
not  many  years  ago  Plante  discovered  that  when  an  arrange- 
ment composed  of  lead  plates,  having  their  outer  surfaces 
reduced  to  a spongy  form,  and  immersed  in  dilute  sulpliuric 
acid,  was  traversed  by  an  electric  current,  the  resulting 
chemical  changes  transformed  it  into  a battery,  so  that 
when  the  charging  circuit  was  interrupted,  and  the  plates 


ELECTRICAL  ENERGY 


211 


which  had  been  connected  to  the  two  terminals  of  the 
dynamo,  or  primary  battery,  used  for  charging,  were  con- 
nected with  each  other,  an  electric  current  was  produced, 
accompanied  by  a gradual  restoration  of  the  cell  to  its  origi- 
nal condition,  and  that  when  this  was  attained  the  current 
stopped. 

The  name  of  secondary  battery  or  accumulator  has  been 


Fig.  66. 


given  to  a cell  of  this  kind,  which  acquires  the  property 
of  producing  an  electric  current  by  having  a current  passed 
into  it.  The  original  Plantd  accumulator  has  been  consider- 
ably improved  by  Faure  and  others,  and  one  of  these  cells, 
as  now  constructed  by  the  Electrical  Power  Storage  Com- 
pany, is  shown  in  Fig.  66. 

The  plates  are  made  of  sheets  of  lead  perforated  with  a 
number  of  square  pyramidal  holes,  filled  up,  in  alternate 


212 


ELECTRICITY  IN  MODERN  LIFE 


plates,  with  a paste  made  of  red  lead  and  sulphuric  acid, 
and  litharge  and  sulphuric  acid  respectively. 

The  terms  accumulator  and  storage  battery  are  now  in 
very  general  use,  but  the  reader  should . bear  in  mind  that 
what  is  stored  up  is  not  electricity,  but  electrical  energy — 
that  is  to  say,  the  power  of  producing  an  electric  current. 
Storage  batteries  may  be  used  instead  of  transformers  in  dis- 
tributing the  current  from  the  central  station,  but,  as  they 
require  skilled  attention,  they  cannot  be  placed  in  the 
houses  of  consumers,  and  therefore  have  to  be  distributed 
among  sub-stations,  each  of  which  supplies  a group  of  houses 
in  its  immediate  neighborhood. 

The  cells  at  each  sub-station  are  connected  up  into  a 
series  of  groups  arranged  in  series — that  is  to  say,  with  the 
positive  plate  of  one  cell  in  connection  with  the  negative 
plate  of  the  next,  and  so  on;  and  in  order  to  charge  the 
battery,  the  high  potential  current  from  the  central  station 
is  allowed  to  flow  into  a set  of  several  groups  coupled  up 
in  series. 

When  the  batteries  are  charged  the  groups  are  discon- 
nected and  connected  up  in  parallel — that  is,  all  the  nega- 
tive terminals  connected  together,  and  likewise  the  positive 
terminals,  the  cells  in  each  group  being  still  connected  in 
series.  The  number  of  cells  in  a group  is  regulated  so  as 
to  give  a current  of  the  desired  electro-motive  force  from 
the  sub-station  to  the  consumers.  The  current  provided 
in  this  way,  being  continuous  in  direction,  is  valuable,  not 
only  for  electric  lighting,  but  for  driving  motors  or  electro- 
plating. Alternating  currents  are  not  at  present  used  for 
working  electro -motors,  as  no  satisfactory  form  of  motor 
has  yet  been  devised  to  work  with  such  currents.  The 
mains  carrying  the  currents  from  a central  station  may 


ELECTRICAL  ENERGY 


213 


either  be  carried  overhead  on  poles  or  laid  underground. 
In  towns  they  are  usually  carried  underground,  as  the 
heavy  cables  required  to  carry  large  currents  are  not  only 
unsightly  when  carried  overhead,  but  form  a source  of 
danger  in  case  of  breakage,  owing  to  their  great  weight, 
' and  to  the  fact  that  they  carry  currents  dangerous  to  life. 
Distribution  by  means  of  accumulators  has  the  advantage 
of  enabling  the  electro-motive  force  to  be  kept  extremely 
constant,  and  this  is  of  the  greatest  importance  in  electric 
lighting,  as  any  variation  in  the  electro-motive  force  causes 
a fluctuation  or  flickering  in  the  light.  Another  great  ad- 
vantage of  the  system  of  distribution  by  means  of  accumu- 
lators is  that  a much  smaller  plant  is  required  at  the  central 
station,  because,  under  ordinary  circumstances,  the  demand 
for  current  will  be  much  greater  at  certain  periods  out  of  the 
twenty-four  hours  than  at  others,  and  when  accumulators 
are  used  the  dynamos  can  be  kept  at  work  charging  them 
during  the  time  when  the  demand  is  slack,  thereby  storing 
up  energy  to  meet  the  heavy  demand  during  the  busier  part 
of  the  day.  When  the  distribution  is  effected  by  means  of 
transformers,  sufficient  engines  and  dynamos  have  to  be 
provided  to  meet  the  greatest  demand  that  can  possibly 
be  made  upon  the  station,  and  arrangements  have  to  be 
made  for  throwing  additional  dynamos  into  the  circuit  as 
the  number  of  lamps  turned  on  increases,  and  this  has 
to  be  done  without  causing  any  flickering  in  the  lights, 
which  would  be  a great  annoyance  to  consumers. 

The  disadvantages  of  accumulators  are — their  high  initial 
cost,  the  expense  of  maintenance  and  renewal,  which  is 
considerable,  and  the  fact  that  they  waste  a much  larger 
proportion  of  electrical  energy  than  is  done  by  a well- 
constructed  transformer. 


214 


ELECTRICITY  IN  MODERN  LIFE 


There  is  aaother  method  for  using  current  in  the  mains 
of  a higher  electro-motive  force  than  is  suitable  for  incan- 
descent lamps  or  electro-motors,  consisting  in  the  employ- 
ment of  a special  method  of  distribution,  known  as  the 
three-wire  system,  which  was  patented  by  Dr.  Hopkinson 
in  the  year  1882. 

It  is  only  applicable  to  the  distribution,  at  comparatively 
low  pressure,  of  continuous  currents,  and  is  therefore  not 
suitable  for  use  at  central  stations  which  have  to  supply 
large  districts.  It  is  of  great  value,  however,  when  all  the 
houses  supplied  are  included  within  a small  area. 

It  is  not  in  that  case  necessary  to  employ  a very  high 
pressure  in  the  mains,  but  it  is  of  great  advantage  to  employ 
a higher  one  than  can  be  applied  directly  to  the  lamps. 
For  example,  the  highest  E.M.F.  at  which  glow-lamps 
have  been  constructed  to  work  is  100  volts,  and  by  means 
of  the  three-wire  system  a pressure  of  some  200  volts  may 
be  employed  in  the  mains.  This  is  advantageous  in  two 
ways.  In  the  first  place,  it  reduces  the  effect  of  small  varia- 
tions of  potential  at  the  dynamo  terminals.  For  example,  in 
the  case  considered,  a variation  of  5 per  cent  in  the  E.M.F. 
in  the  mains  would  produce  a variation  of  only  2i  per  cent 
at  the  lamp  terminals,  so  that  the  lamps  would  burn  much 
more  steadily.  It  also  enables  a much  smaller  weight  of 
copper  to  be  employed  in  the  mains,  and  thereby  greatly 
reduces  the  cost  of  the  installation,  and  enables  the  light 
to  be  supplied  with  profit  at  a lower  rate  than  would  other- 
wise be  possible. 

In  this  system  two  dynamos  are  employed,  the  negative 
terminal  of  one  being  attached  to  one  main,  called  the  nega- 
tive main,  and  the  positive  terminal  of  the  second  dynamo 
to  the  other,  or  positive,  main.  The  other  terminals  of  the 


ELECTRICAL  ENERGY 


215 


two  dynamos  are  attached  to  a separate  main  known  as 
the  balanciDg  wire,  and  the  lamps  and  motors  each  have 
one  of  their  terminals  connected  with  this  balancing  wire, 
while  the  others  are  attached,  in  as  nearly  as  possible  equal 
proportions,  to  the  positive  and  negative  main  respectively. 
If  the  resistances  of  the  lamps  and  motors  in  the  two  circuits 
are  exactly  equal  there  will  be  no  current  along  the  balanc- 
ing wire,  and  the  greater  the  inequality  the  greater  will 
be  the  current  along  this  main.  As  the  balancing  wire  has 
to  carry  much  less  current  than  the  other  two  mains  it  is 
made  much  smaller,  and  this  system  of  distribution  is  found 
to  effect  a considerable  saving  in  the  amount  of  copper 
necessary  for  the  mains. 

When  the  electric  current  is  carried  from  a central  station 
to  houses  at  a considerable  distance  the  electro-motive  force 
gradually  diminishes  as  the  distance  from  the  station  in- 
creases, and,  as  has  been  explained  in  a previous  chapter, 
the  fall  of  potential  between  any  two  points  is  proportional 
to  the  resistance  between  them;  so  that,  if  a good  many 
consumers  are  supplied  from  different  points  of  the  same 
main,  the  lamps  of  those  at  a greater  distance  will  not  be 
nearly  as  bright  as  those  close  to  the  station.  In  order 
to  remedy  this  defect  as  far  as  possible,  a system  of  feeders 
should  be  employed — that  is  to  say,  a series  of  mains  should 
be  provided  running  from  the  central  station  to  various  dis- 
tant portions  of  the  house  mains,  no  current  being  taken 
off  at  any  intermediate  portion  of  the  feeder. 

This  system  is  extensively  used  on  the  Continent  with 
very  satisfactory  results,  but  hitherto  it  has  not  been  very 
generally  introduced  into  this  country.  When  street  lamps 
are  lighted  by  electricity  the  current  is  usually  supplied  at 

an  annual  charge  for  each  lamp,  definite  stipulations  of 

Science — Vol.  XIII — 10 


216 


ELECTRICITY  IN  MODERN  LIFE 


course  being  made  as  to  the  number  of  hours  during  which 
the  lamps  are  to  be  kept  alight.  In  private  houses,  how- 
ever, or  in  factories  or  workshops  where  the  current  is  used 
either  for  giving  light  or  for  working  electro-motors,  the 
current  is  usually  charged  for  according  to  the  amount 
consumed. 

Meters  which  measure  the  amount  of  current  passed 
through  them,  just  as  gas-meters  measure  the  amount  of 
gas,  are  fixed  in  the  houses;  but  these  meters  do  not,  as 
in  the  case  of  gas-meters,  absolutely  insure  the  consumers 
getting  what  they  pay  for,  for  the  electrical  energy  obtain- 
able from  the  current  depends  on  the  electro-motive  force 
as  well  as  on  the  quantity,  so  that  if  the  former  is  allowed 
to  fall  below  a certain  value  the  consumer  will  be  paying 
too  high  a price  for  his  supply.  Unfortunately,  no  com- 
pletely satisfactory  simple  meter  has  yet  been  devised 
for  measuring  electrical  energy  instead  of  simple  current 
strength;  but  a good  many  inventors  are  working  at  the 
subject,  and  we  may  hope  that  before  long  they  will  be 
successful  in  producing  a simple  and  efficient  meter  of  the 
kind  so  urgently  required. 

The  different  forms  of  meter  employed  for  measuring 
the  amount  of  current  supplied  are  far  too  numerous  for 
me  to  attempt  to  give  a detailed  description  of  them,  for 
hardly  a week  passes  without  a new  one  being  patented. 

The  first  current-meter  was  invented  by  Edison,  who 
exhibited  it  at  the  Paris  Exhibition  in  1881,  since  which 
time  it  has  been  very  largely  employed  in  measuring -cur- 
rents supplied  from  central  stations.  In  its  original  form 
this  meter  consisted  of  a pair  of  copper  plates  suspended 
from  the  ends  of  a balanced  beam,  and  dipping  into  a solu- 
tion of  sulphate  of  copper- 


ELECTRICAL  ENERGY 


217 


A continuous  current  passing  through  the  solution  car- 
ried the  copper  from  one  plate  and  deposited  it  upon  the 
other  until  the  difference  of  weight  was  sufficient  to  tip  over 
the  balanced  beam.  When  this  happened  it  was  registered 
by  means  of  a counting  mechanism,  and  at  the  same  time 
the  direction  of  the  current  through  the  meter  was  reversed, 
so  that  the  copper  was  carried  from  the  heavy  to  the  light 
plate  until  the  latter  became  heavy  enough  to  tip  up  the 
beam  and  again  reverse  the  current. 

In  this  way  the  process  went  on  continuously.  The 
whole  of  the  lighting  current  was  not  sent  through  the  meter, 
for  unless  this  were  to  be  made  of  immense  size  the  resist- 
ance would  be  so  great  as  to  reduce  considerably  the  strength 
of  the  current,  and  therefore  the  meter  was  attached  as  a 
shunt  to  the  main  circuit,  and  was  traversed  only  by  a frac- 
tion of  the  whole  current. 

The  meter  in  this  form  was,  however,  found  to  be  open 
to  serious  objections.  The  resistance  of  electrolytes  is 
always  found  to  diminish  as  the  temperature  increases, 
while  that  of  metallic  conductors  increases  with  the  tem- 
perature. In  hot  weather,  therefore,  the  resistance  of  the 
sulphate  of  copper  would  be  diminished,  while  that  of 
the  copper  lead  would  be  increased,  causing  a larger  pro- 
portion of  the  total  current  to  go  through  the  meter  in  hot 
weather  than  in  cold. 

. The  making  and  breaking  of  contact  necessitated  by  the 
use  of  a commutator,  for  reversing  the  current,  also  led  to . 
endless  trouble,  so  that  the  meter  had  to  be  modified,  and 
in  its  present  form  zinc  plates  dipping  into  a solution  of 
sulphate  of  zinc  are  employed.  The  plates  are  examined 
and  weighed  once  a month,  and  fresh  ones  are  inserted  as 
the  old  ones  are  worn  out.  A thousandth  part  of  the  total 


218 


ELECTRICITY  IN  MODERN  LIFE 


current  is  usually  sent  through  the  meter;  and  the  propor- 
tion of  current  going  through  the  meter  is  maintained  fairly 
constant  within  a considerable  range  of  temperature,  by 
placing  a copper  resistance  in  series  with  the  solution,  so 
that  when  the  temperature  rises  the  increase  in  the  resistance 
of  the  copper  may  balance  the  decrease  in  the  resistance  of 
the  solution.  The  alternative  path  of  the  current  is  made 
of  German  silver,  the  resistance  of  which  changes  very  little 
with  the  temperature.  These  meters  may  be  depended  on 
to  about  3 per  cent,  and  are  in  very  general  use. 

Professors  Ayrton  and  Perry  have  designed  an  entirely 
different  type  of  meter  intended  to  fulfil  the  condition,  the 
desirability  of  which  I have  already  pointed  out,  of  measur- 
ing the  electrical  energy  directly  instead  of  merely  the 
strength  of  the  current. 

The  instrument  consists  essentially  of  a good  clock, 
the  pendulum  bob  of  which  is  formed  of  a coil  having  a 
resistance  of  about  a thousand  ohms.  A coil  of  short  thick 
wire,  having  only  a small  resistance,  is  fixed  to  the  clock 
case,  parallel  to  the  coil  forming  the  pendulum  bob. 

The  current,  as  it  enters  the  house,  passes  through  this 
coil  of  thick  wire,  from  which  it  is  carried  to  the  lamps, 
motors,  or  other  electric  machinery  in  the  house,  and  then 
passes  away  to  the  street  main,  or  to  another  house.  The 
terminals  of  the  fine  wire  coil  of  the  pendulum  pass  up  the 
pendulum  rod,  and  one  of  them  is  connected  to  the  terminal 
of  the  thick  wire  coil  where  the  current  enters,  the  other 
being  connected,  by  means  of  a fine  wire,  to  the  house 
main  where  it  leaves  the  house. 

The  current  passing  through  the  pendulum  bob  will  then 
depend  on  the  diflierence  of  the  electro-motive  forces  in  the 
main,  where  it  enters  and  leaves  the  house  respectively. 


ELECTRICAL  ENERGY 


219 


whereas  the  current  passing  through  the  thick  wire  coil  is 
practically  equal  to  the  total  current  working  the  lamps  and 
motors.  Now  the  amount  of  energy  absorbed  in  the  house 
is  proportional  to  the  product  of  the  strengths  of  these  two 
currents,  and  whatever  variation  may  take  place  either 
in  the  strength  of  the  current,  or  in  the  electric  pressure, 
the  loss  of  the  clock  in  that  time,  due  to  the  mutual  actions 
of  the  currents,  will  be  exactly  proportional  to  the  amount  of 
energy  absorbed.  This  meter  has  been  somewhat  modified 
and  improved  by  Dr.  Aron  in  Germany,  and  is  used  in  con- 
nection with  the  Berlin  central  stations. 

Among  the  meters  which  have  been  designed  for  use 
with  alternating  currents  I will  only  mention  two  as 
types. 

The  first  of  these  has  recently  been  devised  by  Mr. 
Schallenberger,  electrician  to  the  Westinghouse  Company 
at  Pittsburg,  in  the  United  States.  It  consists  essentially 
of  a circular  iron  disk  mounted  upon  a vertical  axis,  and 
connected  with  a train  of  mechanism  to  count  its  revolutions. 
A coil  of  wire  carrying  the  current  to  be  measured  is  wound 
round  one  of  the  diameters  of  this  disk,  and  a second  coil, 
having  its  terminals  connected  together,  so  as  to  form  a com- 
plete circuit  in  itself,  is  wound  round  a second  diameter, 
which  is  inclined  to  the  first  at  an  angle  of  45°.  When  the 
alternating  current  is  sent  from  the  first  coil  a series  of 
secondary  currents  are  produced  in  the  other.  Now  the 
main  current  will  at  any  moment  magnetize  the  iron  disk 
in  a certain  way,  and,  as  the  result  of  this  magnetization, 
the  secondary  current  induced  in  the  other  coil  will  make 
the  disk  begin  to  rotate.  When  the  primary  current  falls 
to  zero  the  induced  current  will  magnetize  the  disk,  and  the 
arrangement  is  such  that  the  reaction  between  this  magneti- 


220 


ELECTRICITY  IN  MODERN  LIFE 


zation  and  the  following  current  in  the  circuit  will  continue 
to  cause  rotation  in  the  same  direction. 

The  other  meter  was  invented  by  Professor  Forbes,  and 
is  suited  for  the  measurement  either  of  continuous  or  alter- 
nating currents,  as  its  indications  depend  on  the  amount  of 
heat  developed  by  the  current  passing  through  a short  spiral 
coil  of  thick  wire  fixed  horizontally  within  the  meter.  The 
heating  of  this  coil  sets  up  convection  currents  in  the  air, 
which  turn  a sort  of  small  windmill  arrangement  fixed  above 
the  coil.  The  vertical  axis  about  which  the  windmill  turns 
is  connected  with  a train  of  wheelwork  which  serves  to 
count  the  revolutions,  and  the  amount  of  current  which 
has  passed  through  the  meter  will  therefore  be  known  when 
the  relation  between  the  total  amount  of  current — viz.,  the 
product  of  the  current  strength  by  the  time — and  the  number 
of  revolutions,  has  been  determined  once  for  all. 


ELECTRIC  LIGHTING 


221 


CHAPTER  XV 

ELECTRIC  LIGHTING 

IF  a strong  electric  current,  such  as  may  be  obtained 
from  a dozen  or  more  Grrove  cells,  is  passed  through 
a circuit  containing  two  pieces  of  carbon  in  contact 
with  each  other,  the  resistance  at  the  point  of  contact  is 
so  great  that  the  carbons  will  become  white  hot.  If  they 
are  then  separated  a short  distance  an  arc  of  light  will  be 
formed  between  them,  the  carbon  in  the  meantime  gradu- 
ally burning  away,  especially  the  one  in  connection  with 
the  positive  terminal  of  the  battery.  When  the  distance 
between  the  two  carbon  points  exceeds  a certain  amount, 
depending  on  the  electro-motive  force  in  the  circuit,  the 
arc  will  be  extinguished,  and  cannot  be  obtained  again 
until  the  carbons  are  brought  into  actual  contact,  as  the 
electro-motive  force  of  the  battery  is  not  sufficient  to  drive 
a current  through  an  appreciable  thickness  of  air  resistance, 
though  it  can  maintain  the  current  across  the  arc  when  this 
is  once  formed,  owing  to  the  resistance  of  an  arc  of  a given 
length  being  incomparably  less  than  that  of  the  same  length 
of  cool  air. 

For  a good  many  years  light  obtained  in  this  way  has 
been  used  to  a considerable  extent  when  a very  strong  light 
was  required  for  lecture  experiments,  and  sometimes  also 


222 


ELECTRICITY  IN  MODERN  LIFE 


for  magic  lantern  exhibitions,  when  cost  was  not  a matter 
of  great  importance.  As,  however,  independently  of  the 
initial  cost  of  the  batteries,  the  zinc  and  acid  used  in  main- 
taining a single  bright  arc  light  for  a few  hours  might  cost 
from  ten  shillings  to  a pound,  it  is  clear  that  it  would  be 
quite  hopeless  to  think  of  employing  the  electric  light 
obtained  in  such  a manner  for  general  lighting  purposes. 

The  invention  of  the  dynamo,  however,  makes  it  possi- 
ble to  produce  electric  current  by  the  consumption  of  the 
comparatively  cheap  fuel,  coal,  instead  of  the  more  costly 
zinc,  which  is  the  fuel  usually  employed  in  primary 
batteries. 

There  are  two  distinct  systems  of  electric  lighting 
adapted  to  meet  totally  different  requirements — viz.,  the 
systems  known  respectively  as  Arc  Lighting  and  Incan- 
descent Lighting. 

Arc  Lighting. — The  electric  arc  which  I have  just  de- 
scribed gives  an  exceedingly  powerful  light,  and  when 
protected  by  globes  of  opal  glass  or  other  translucent  sub- 
stance, to  shade  the  eye  from  the  direct  glare  of  the  light, 
it  is  extremely  suitable  for  street  lighting  and  for  use  in 
railway  stations,  factories,  and  other  large  buildings. 

The  number  of  different  kinds  of  arc  lamp  is  almost 
innumerable,  but  those  employed  for  ordinary  lighting  pur- 
poses are  invariably  automatic — that  is  to  say,  they  are 
provided  with  some  arrangement  by  means  of  which  the 
carbon  points,  as  they  burn  away,  can  be  maintained  at 
an  approximately  constant  distance  apart.  The  only  way 
of  doing  this  that  has  really  proved  a practical  success 
consists  in  the  use  of  some  electro-magnetic  arrangement, 
according  to  which,  when  the  distance  becomes  too  great, 
the  weakening  of  the  current,  Dy  diminishing  the  magneti- 


ELECTRIC  LIGHTING 


223 


zation  of  a small  electro-magnet,  allows  its  armature  to  fall, 
and  sets  in  motion  a train  of  mechanism  by  which  the  car- 
bon points  are  made  to  approach  each  other,  thereby  di- 
minishing the  resistance,  so  that  the  current  is  again  able 
to  magnetize  the  electro-magnet  sufficiently  to  stop  the 
mechanism. 

The  lamps  employed  at  the  time  when  the  electric  light 
was  only  used  for  lecture  purposes  were  exceedingly  com- 
plicated in  structure,  and  were  moreover  very  unsatisfac- 
tory, as  the  regulation  was  far  from  perfect,  the  light  at 
times  becoming  dim  and  then  suddenly  flashing  out  into 
its  original  brilliancy.  Most  of  those,  however,  which  are 
now  in  use  are  very  satisfactory,  as  may  be  seen  from  the 
steadiness  of  the  arc  lamps  in  any  well-managed  installation. 

Arc  lamps  are  usually  connected  together  in  series,  and 
are  supplied  with  a constant  current.  Many  of  the  circuits 
are  of  a considerable  length,  some  in  America  attaining  to  as 
great  a length  as  twelve  miles,  while  circuits  of  eight  miles 
in  length  are  frequently  employed  by  the  Thomson-Houston 
Company,  who  have  carried  out  a very  large  number  of  in- 
stallations both  in  America  and  in  Europe.  The  steadiness 
of  the  light  will  not  only  depend  upon  the  mechanism  of  the 
lamps,  but  quite  as  much  upon  the  mechanical  and  electrical 
governors  employed  for  maintaining  the  constancy  of  the 
current.  Defects  in  the  regulating  apparatus  are  chiefly 
noticeable  when  lamps  are  switched  into  or  out  of  the  cir- 
cuit, as,  in  order  to  prevent  fluctuations  in  the  light,  the 
governing  apparatus  must  be  sufficiently  sensitive  to  cause 
the  dynamo  to  respond  at  once  to  the  demand  made  upon 
it  for  extra  current,  or  to  supply  a smaller  current  when 
the  load  is  diminished,  and  even  if  the  electrical  govern- 
ing system  is  all  that  can  be  desired,  the  engine  governor 


224 


ELECTRICITY  IN  MODERN  LIFE 


must  likewise  be  extremely  sensitive,  so  as  to  enable  the 
engine  to  begin  at  once  to  supply  the  extra  amount  of 
work  when  additional  lamps  are  thrown  into,  the  circuit, 
or  to  supply  less  work  when  lamps  are  cut  out.  If  the 
lamps  are  supplied  from  accumulators,  then  of  course  the 
regulation  of  the  engine  ceases  to  be  a matter  of  primary 
importance.  The  number  of  lamps  included  in  any  one 
dynamo  circuit  will  depend  of  course  upon  the  capacity 
of  the  dynamo,  upon  the  current  absorbed  by  each  lamp, 
and  upon  the  difference  of  potential  which  is  to  be  main- 
tained between  its  terminals.  The  quality  of  the  carbons 
also  exerts  an  important  effect  on  the  steadiness  of  the 
light  unless  the  electrical  regulation  is  extremely  good. 

The  first  experiments  on  the  production  of  an  electric 
arc  between  carbon  points  were  made  by  Sir  Humphry 
Davy  with  carbons  consisting  simply  of  sticks  of  wood 
charcoal,  but  it  was  soon  found  that  this  material  was^ 
much  too  soft  for  the  purpose,  as  it  burned  very  rapidly, 
giving  off  numerous  sparks.  Eecently,  however,  Gaudin 
has  gone  back  to  the  use  of  rods  of  wood  charcoal,  which, 
however,  have  their  density  very  greatly  increased  by  being 
soaked  in  some  liquid  hydrocarbon,  in  order  to  fill  up  their 
pores,  and  are  then  fired,  the  process  being  repeated  until 
the  desired  density  is  obtained.  The  first  improvement  in 
the  carbons  used  for  producing  the  electric  arc  is  generally 
considered  to  have  been  made  by  Foucault,  and  consisted  in 
replacing  the  rods  of  wood  charcoal  by  rods  sawed  out  of 
gas  carbon.  The  principal  points  which  have  to  be  aimed 
at  in  the  manufacture  of  carbons  for  arc  lighting  are,  in  the 
first  place,  to  obtain  a carbon  of  regular  density,  of  as  low 
electrical  resistance  as  possible,  and  free  from  admixture 
with  other  substances;  and  in  the  second  place,  to  produce 


ELECTRIC  LIGHTING 


225 


rods  of  sufficient  length  to  burn  as  long  as  may  be  required, 
perfectly  straight  and  cylindrical  in  form.  Various  proc- 
esses are  employed  to  attain  these  results,  and  the  manu- 
facturers usually  do  their  best  to  keep  them  secret;  but  the 
general  procedure  in  all  of  them  consists  in  first  reducing 
coke  or  graphite  to  a fine  powder,  and  then  washing  it  with 
an  alkaline  solution,  to  free  it  from  silica  and  earthy  im- 
purities; after  this  it  is  formed  into  a stiff  paste  by  mixing 
it  with  a sufficient  quantity  of  some  tarry  hydrocarbon,  and 
the  paste  is  then  forced  under  pressure  into  molds  of  the 
required  form.  When  the  rods  are  taken  out  of  the  molds 
they  are  dried  and  packed  in  air-tight  boxes,  the  empty 
spaces  between  the  rods  being  filled  up  with  coke  dust, 
after  which  they  are  fired  in  a kiln.  It  is  generally  found 
necessary  to  repeat  the  process  of  soaking  in  hydrocarbon, 
with  the  subsequent  firing,  at  least  twice,  and  in  the  case 
of  the  best  carbons  it  is  usually  repeated  several  times. 

When  a sufficiently  sensitive  system  of  electric  govern- 
ment is  employed,  very  good  results  can  be  obtained  even 
with  inferior  carbons,  and  many  of  my  readers  will  probably 
remember  the  lighting  of  the  American  and  Italian  Exhibi- 
tions in  London  in  1887  and  1888,  which  were  carried  out 
on  the  Thomson-Houston  system;  and  although  the  com- 
monest American  compressed  carbons  were  employed,  the 
steadiness  of  the  light  was  everything  that  could  be  desired. 

Arc  lights  are  extremely  suitable  for  use  in  lighthouses, 
as  the  great  brilliancy  of  the  light  enables  it  to  be  seen  at 
a considerable  distance,  even  in  foggy  weather.  This  was 
recognized  at  a comparatively  early  period,  and  before  the 
invention  of  the  modern  dynamo,  which  first  made  possible 
the  general  introduction  of  the  electric  light,  several  of  the 
more  important  lighthouses  were  provided  with  arc  lights, 


226 


ELECTRICITY  IN  MODERN  LIFE 


the  current  of  which  was  supplied  from  large  magneto  ma- 
chines, built  up  of  a great  number  of  permanent  magnets, 
with  coils  revolving  between  them.  Most  of  our  ironclads 


Fig.  67. 


are  now  supplied  with  powerful  arc  lights,  provided  with 
reflectors,  and  known  as  search-lights,  to  enable  them  to 
discover  the  presence  of  torpedo  boats,  and  to  destroy 


Science^  228 


f 


LIBRARY 
OF  THE 

i!?^:vE?:siTV  0?  Illinois 


ELECTRIC  LIGHTING 


227 


them,  by  aid  of  their  quick-firing  guns,  before  they  have 
got  near  enough  to  do  any  damage. 


Fia.  68. 


What  are  known  as  hand-feed  lamps  are  usually  em- 
ployed for  search-lights — viz.,  lamps  in  which  the  carbons 


228 


ELECTRICITY  IN  MODERN  LIFE 


are  manipulated  by  hand  instead  of  by  an  automatic  ar- 
rangement. Fig.  67  illustrates  a simple  form  of  hand-feed 
lamp,  manufactured  by  Messrs.  Ernest  Scott  & Co.,  of  New- 
castle, and  designed  for  search-lights,  or  for  use  with  micro- 
scopes or  magic  lanterns. 

For  use  as  search-lights  these  hand-feed  lamps  are  pro- 
vided with  a system  of  lenses  for  concentrating  the  light 
into  a single  beam.  The  whole  arrangement  is  mounted  in 
such  a way  as  to  allow  of  the  beam  being  thrown  in  any 
direction  required.  A simple  form  of  projector,  as  an  ap- 
paratus of  this  kind  is  called,  manufactured  by  Messrs. 
Scott,  is  shown  in  Fig.  68. 

Arc  lights  are  also  employed  to  a considerable  extent 
as  signals  on  board  large  passenger  steamers  and  yachts 
which  have  electric  lighting  machinery  on  board,  as  is 
now  generally  the  case,  most  of  the  more  important  pas- 
senger steamers  and  the  larger  yachts  having  their  saloons 
and  cabins  lighted  by  incandescent  electric  lamps. 

A great  many  makers  have  designed  very  compact  com- 
binations of  engines  and  dynamos  intended  specially  for  use 
on  board  ship,  where  space  is  limited,  and  one  of  these  is 
shown  in  Fig.  69,  which  illustrates  a combination  manu- 
factured by  Messrs.  Mather  & Platt,  of  Manchester,  con- 
sisting of  a very  effective  and  compact  form  of  dynamo, 
known  as  the  “Manchester  Dynamo,’’  driven  from  a double- 
cylinder diagonal  engine,  by  means  of  a short  belt  provided 
with  tightening  gear,  as  shown  in  the  illustration. 

Another  very  interesting  application  of  arc  lighting  to 
shipping  purposes  is  afforded  by  the  arrangements  which 
have  been  adopted  within  the  last  few  years  for  making 
the  passage  of  the  Suez  Canal  at  night, 

Up  to  the  year  1886  no  night  traffic  through  the  canal 


ELECTRIC  LIGHTING 


229 


was  permitted,  but  in  that  year  it  was  decided  to  allow 
vessels  of  war  and  those  carrying  mails,  if  furnished  with 
electric  lights  in  accordance  with  the  regulations  laid  down 
by  the  canal  company,  to  traverse  at  night  any  portion  of 
the  canal  between  Port  Said  and  the  Mediterranean  entrance, 
about  a third  of  the  entire  distance.  The  first  vessel  which 
availed  itself  of  this  permission  was  the  steamship  ‘‘Car- 
thage,” belonging  to  the  Peninsular  and  Oriental  Steam 
Navigation  Company,  which  made  the  passage  by  tbe  aid 
of  the  electric  light  with  perfect  success  in  April,  1886, 
and  the  example  was  followed  shortly  afterward  by  other 
vessels  with  such  success  that  the  company  decided  to  ex- 
tend the  permission  to  all  vessels,  and  at  the  same  time, 
by  providing  beacons  and  light-buoys,  to  guide  the  vessels 
during  the  night  passage,  navigation  by  night  was  made 
possible  throughout  the  whole  canal. 

The  company  stipulates  that  all  vessels  availing  them- 
selves of  this  permission  should  be  provided  with  a pro- 
jector search-light,  fitted  upon  a platform  large  enough  to 
accommodate  a man  to  manipulate  the  light,  the  platform 
being  connected  to  the  vessel  as  near  to  the  water’s  edge 
as  possible,  and  an  automatic  electric  lamp  suspended  upon 
the  bridge,  capable  of  illuminating  an  area  two  hundred 
yards  in  diameter  round  the  vessel.  The  man  on  the  plat- 
form regulates  the  position  of  the  carbons  of  the  search- 
lamp  by  hand,  and  at  the  same  time  he  depresses  or  deflects 
the  light  to  either  side  in  accordance  with  the  orders  of  the 
pilot  upon  the  bridge,  the  orders  being  usually  given  by 
means  of  a telephone. 

The  placing  of  the  projector  close  to  the  edge  of  the 
water,  so  that  the  light  may  be  hidden  under  the  bow  of 
the  ship,  is  an  essential  point,  for  any  direct  rays  of  light 


230 


ELECTRICITY  IN  MODERN  LIFE 


intervening  between  the  pilot  and  the  distant  illuminated 
object,  by  means  of  which  he  is  steering  the  vessel,  would 
dazzle  his  eyes.  Fig.  70  shows  a vessel  so  fitted  passing 
through  the  canal. 

The  lamp  suspended  over  the  bridge  lights  up  the  whole 
deck  of  the  vessel  and  the  canal  with  its  banks  on  either 
side,  and  is  only  intended  for  use  when  passing  other  ves- 


Fig.  70. 


sels  which  are  tied  up  at  the  passing-stations,  or  to  provide 
light  for  a vessel  thus  tied  up  in  order  to  allow  another  one 
to  pass.  Several  of  the  chief  coaling  firms  at  Port  Said 
have  now  provided  themselves  with  sets  of  portable  electric 
lighting  plants  fulfilling  the  requirements  of  the  company’s 
regulations,  and  any  vessel  which  does  not  possess  a plant 
of  its  own  may  hire  one  of  these  for  a fee  of  £10. 

Electric  Gandies, — Before  passing  on  to  describe  the  sys- 


ELECTRIC  LIGHTING 


231 


tern  of  incandescent  electric  lighting  I mast  not  omit  to 
mention  the  JablochkoflE  electric  candle. 

This  consists  of  a pair  of  carbon  rods,  placed  side  by 
side,  and  separated  by  a strip  of  insulating  material,  usually 
consisting  of  a kind  of  porcelain.  The  current  passes  up 
one  carbon  and  down  the  other,  forming  an  arc  at  the  top, 
and  the  porcelain  gradually  burns  away  with  the  carbons. 

In  order  to  start  the  arc  when  the  current  is  turned  on, 
the  top  of  the  candle  is  generally  tipped  with  a paste  made 
of  powdered  carbon  and  gum.  The  Jablochkoff  candle  is 
of  considerable  interest  historically,  as  it  was  employed  in 
lighting  up  the  Avenue  de  L’ Opera  in  Paris  in  1878,  which 
was  the  first  example  of  street  lighting  by  means  of  elec- 
tricity. It  was  also  employed  on  the  Victoria  Embankment 
in  London,  and  in  many  other  places. 

In  the  case  of  the  current  being  accidentally  interrupted 
the  candles  will  go  out,  and  they  will  not  reignite  them- 
selves; but  a still  more  serious  defect  is  that  the  resistance 
of  the  arc  undergoes  constant  variation  owing  to  impurities 
and  variations  in  the  density  of  the  porcelain,  so  that  the 
light  is  extremely  unsteady. 

Some  modifications  of  Jablochkoff ’s  original  candle  have 
been  devised  in  order  to  overcome  these  defects,  and  in 
some  cases  with  considerable  success,  but  their  use  is  not 
sufficiently  extensive  for  it  to  be  necessary  for  me  to  describe 
them  here. 

Incandescent  Lighting, — Arc  lamps  are  not  at  all  suitable 
for  the  lighting  of  rooms  in  dwelling-houses,  or  for  the 
lighting  of  the  interiors  of  theatres,  as  the  light  is  far  too 
intense:  what  is  required  for  such  purposes  is  a considerable 
number  of  centres  of  light  of  moderate  intensity,  and  not 
one  or  two  centres  of  very  high  intensity,  such  as  are  given 


232 


ELECTRICITY  IN  MODERN  LIFE 


by  arc  lamps.  This  requirement  is  completely  fulfilled  by 
what  are  known  as  incandescent  or  glow  lamps,  which  more- 
over lend  themselves  exceedingly  well  to  decorative  pur- 
poses, much  better  indeed  than  gas-burners. 

The  principle  of  the  incandescent  lamp  consists  in  pass- 
ing the  current  through  a wire  or  filament  of  some  substance 
which  is  only  fusible  with  difficulty,  and  which  has  a com- 
paratively high  electrical  resistance. 

The  heat  generated  by  the  passage  of  a current  through 
such  a wire,  or  filament,  raises  it  to  a white  heat,  and  pro- 
vides a source  of  light  very  much  whiter  than  ordinary  gas- 
light, and  which  has  many  other  important  advantages  over 
it.  In  the  first  place,  although  the  filament  itself  is  main- 
tained at  an  exceedingly  high  temperature,  a glow-lamp  has 
much  less  heating  effect  in  a room  than  a gas-burner,  be- 
cause the  surface  of  the  heated  filament  is  exceedingly 
small,  and  it  is  inclosed  in  an  exhausted  glass  vessel,  while 
the  gas  flame  is  in  immediate  contact  with  the  air,  and  soon 
distributes  its  heat  over  a room  by  means  of  the  strong 
convection  currents  which  it  sets  up  in  the  air  in  its 
neighborhood. 

The  electric  light  again  can  be  turned  on  or  off  without 
having  to  be  lighted,  so  that  the  light  can  be  turned  on  as 
one  enters  a room  by  simply  pressing  a button  or  turning 
a switch  near  the  door;  and  if  light  is  wanted  in  a bedroom 
at  night  it  can  be  turned  on,  without  the  slightest  danger, 
by  means  of  a switch  which  can  be  reached  from  the  bed. 

The  greatest  advantage,  however,  of  the  electric  light 
over  illumination  by  means  of  gas  is  the  complete  absence 
of  any  process  of  combustion,  so  that  the  air  in  the  rooms 
in  which  it  is  employed  does  not  become  vitiated  by  the 
absorption  of  oxygen,  and  the  liberation  of  carbonic  acid 


ELECTRIC  LIGHTING 


233 


and  still  more  deleterious  compounds,  such  as  sulphurous 
acid  and  sulphuretted  hydrogen,  which  are  always  formed 
when  gas  is  burned,  and  which  gradually  cause  the  covers 
of  books  in  the  library  to  become  rotten,  discolor  the 
gilding  of  picture-frames,  and  make  it  impossible  to  keep 
most  kinds  of  plants  alive  in  rooms  where  gas  is  burned. 

The  first  electric  glow-lamp  was  invented  by  Demoleyns 
as  far  back  as  the  year  1841,  a platinum  wire  being  em- 
ployed as  the  filament.  In  1845  carbon  was  first  used  for 
the  purpose  by  Starr  of  Cincinnati;  and  in  order  to  prevent 
the  combustion  of  the  carbon  he  placed  it  in  a closed  glass 
vessel,  from  which  the  air  had  been  exhausted,  as  is  now 
invariably  done  in  all  glow-lamps,  whatever  the  material 
employed  for  the  filament.  These  lamps,  however,  were 
invented  before  the  development  of  the  dynamo  had  made 
electric  lighting  possible  on  a commercial  scale,  and  they 
accordingly  dropped  out  of  sight  until,  in  the  year  1873,  the 
Eussian  physicist  Ladiguine  turned  his  attention  to  the  sub- 
ject, and  his  investigations  were  considered  of  such  impor- 
tance that  he  was  presented  with  a prize  by  the  St. 
Petersburg  Academy  of  Sciences.  The  report  which  was 
drawn  up  for  the  occasion  by  the  Eussian  physicist  Wilde 
contains  a very  clear  and  succinct  statement  of  the  advan- 
tages of  carbon  for  glow-lamp  filaments.  Carbon,  said  the 
report,  has,  at  an  equal  temperature,  a greater  radiating 
power  than  platinum,  while  its  thermal  capacity  is  much 
smaller,  so  that  the  same  amount  of  heat  will  raise  a carbon 
filament  to  a much  higher  temperature  than  a platinum 
wire.  Moreover  the  electrical  resistance  of  carbon  is  about 
two  hundred  and  fifty  times  greater  than  that  of  platinum; 
and  the  carbon  may  therefore  be  made  thicker  and  yet  rise 
in  temperature  as  much  as  the  metal.  Carbon,  moreover. 


234 


ELECTRICITY  IN  MODERN  LIFE 


is  infusible,  and  its  temperature  may  therefore  be  raised 
without  any  danger  of  fusion. 

In  the  year  1879  Edison  constructed  a lamp  in  which 
a carbon  filament  was  employed.  It  was  .prepared  by  cut- 
ting small  sheets  of  brown  paper  in  the  form  of  a horseshoe, 
placing  several  of  these  sheets  together,  and  then  heating 
them  to  a high  temperature  in  an  iron  mold.  The  life  of  a 
lamp  provided  with  a filament  of  this  kind  was  however 
very  short,  as  the  carbon  soon  became  disintegrated  by  the 
action  of  the  current.  In  the  year  1880  Edison  improved 
this  lamp  by  substituting  carbonized  bamboo  for  carbonized 
paper;  and  some  improvements  were  introduced  by  Swan, 
who  in  November  of  the  same  year  exhibited  the  first  incan- 
descent lamp  shown  in  England  to  the  Society  of  Telegraph 
Engineers.  Swan’s  carbon  filaments  are  made  of  strings  of 
cotton  about  four  inches  long,,  having  their  ends  enlarged 
by  winding  additional  cotton  round  them.  These  threads 
are  soaked  for  some  time  in  a mixture  of  sulphuric  acid 
and  water,  which  causes  them  to  assume  the  hardness  and 
compactness  of  parchment.  The  filaments  are  then  thor- 
oughly washed,  so  as  to  remove  every  trace  of  acid;  after 
which  they  are  passed  through  dies  with  circular  holes  in 
them,  in  order  to  reduce  them  to  a uniform  cross  section. 
The  filaments  are  then  wound  upon  rods  of  carbon  or 
earthenware,  so  as  to  give  them  the  required  form  before 
carbonization.  They  are  carbonized  by  burying  them  in 
powdered  charcoal  contained  in  a crucible,  and  raising 
them  to  a very  high  temperature  in  a furnace  for  a period 
of  several  hours.  The  filaments  are  mounted  by  having 
their  thick  ends  inserted  into  split  metal  tubes,  which  are 
made  to  clasp  them  tightly  by  means  of  sliding  rings,  the 
arrangement  being  exactly  similar  to  a port-crayon.  Plati- 


ELECTRIC  LIGHTING 


235 


num  wires  are  attached  to  the  upper  ends  of  the  metal  tubes, 
and  pass  out  through  the  glass. 

Edison’s  lamps,  as  improved  by  Swan,  are  now  very 
generally  employed,  being  manufactured  by  the  Edison  and 
Swan  United  Electric  Light  Company,  which  was  formed 
for  working  the  patents  of  these  two  inventors.  The  first 
stage  in  the  manufacture  of  an  Edison-Swan  incandescent 
lamp  consists  in  attaching  the  prepared  filament  to  its  plati- 
num wires,  and  mounting  it  upon  a glass  bridge,  little  beads 


Fig.  71. 


Fig.  72. 


of  glass  being  formed  at  the  same  time  on  the  wires  where 
they  are  to  pass  through  the  walls  of  the  lamp.  The  glass 
globe  is  then  blown  very  much  in  the  shape  of  a pear,  the 
glass  tube  out  of  which  it  is  blown  taking  the  place  of 
the  stem  of  the  pear.  The  lower  portion  of  the  tube  is  then 
cut  off  with  a file,  and  the  carbon,  with  its  platinum  wires, 
fused  into  the  upper  half,  after  which  the  two  portions  of 
the  globe  are  joined  together  by  the  blow-pipe. 

The  lamp  is  then  exhausted  of  air,  first  by  means  of  an 
ordinary  air  pump,  and  finally  by  means  of  a Sprengel  mer- 


236 


ELECTRICITY  IN  MODERN  LIFE 


cury  pump,  with  which  a very  high  vacuum  can  be  obtained. 
Before  the  lamp  is  removed  from  the  Sprengel  pump  it  is 
submitted  to  a process  known  as  flashing. 

This  consists  in  raising  the  filament  to  incandescence  by 
passing  an  electric  current  through  it,  which  expels  any  gas 
that  has  been  absorbed  by  the  carbon,  and  at  the  same  time 
increases  its  density.  The  filament  is  usually  raised  to 
incandescence  and  then  allowed  to  cool,  several  times  in 
succession,  the  process  of  exhaustion  going  on  all  the 

time,  so  as  to  remove  all  the  gases 
that  are  given  out  by  the  filament. 

The  general  appearance  of  the 
lamps  when  completed  is  shown  in 
Figs.  71  and  72,  Fig.  71  showing  a 
lamp  which  is  intended  to  be  hung 
with  the  larger  end  downward  by 
inserting  into  the  two  loops,  attached 
to  the  cap  which  forms  the  termina- 
tion of  the  small  end,  the  ends  of  the 
conducting  wires,  which  are  bent  into 
the  form  of  hooks  for  the  purpose; 
while  Fig.  72  shows  another  lamp 
having  a filament  of  somewhat  different  shape,  and  which 
is  intended  to  be  inserted  in  a holder  such  as  that  shown 


Fig.  73. 


in  Fig.  73. 


Theatre  Lighting. — The  system  of  incandescent  electric 
lighting  presents  special  advantages  for  the  lighting  of 
theatres,  the  most  important  of  which  is  the  almost  abso- 
lute safetv  which  it  provides  against  danger  from  fire,  when 
the  installation  is  properly  carried  out. 

Whether  gas  or  electricity  be  employed,  the  lighting  of 
the  auditorium  can  be  carried  out  just  as  safely  as  that 


ELECTRIC  LIGHTING 


237 


of  an  ordinary  house,  but  the  illumination  of  the  stage  is 
a very  different  matter. 

To  begin  with  the  part  visible  to  the  audience:  the  foot- 
lights, when  gas  is  used,  are  simply  naked  gas-lights,  and 
numerous  accidents  have  occurred  from  the  dresses  of  act- 
resses catching  fire  from  their  approaching  too  near  to  these 
naked  lights.  When  the  electric  light  is  employed  the  foot- 
lights are  all  hermetically  sealed  glass  globes,  which  could 
not  ignite  the  most  flimsy  material,  unless  it  were  left  in 
contact  with  them  for  a considerable  time.  The  principal 
source  of  danger,  however,  is  to  be  found,  not  in  the  foot- 
lights, and  the  permanent  stage  lamps  which  are  attached 
to  battens  suspended  from  the  roof,  but  in  the  movable 
lights  which  are  attached  to  the  different  portions  of  the 
scenery,  being  fixed  to  what  are  sometimes  called  stage- 
ladders,  which  are  hung  on  to  the  movable  scenery  wherever 
they  are  required.  Any  one  who  has  been  behind  the  scenes 
of  a theatre,  and  has  observed  the  close  proximity  of  these 
lights  to  the  inflammable  scenery,  will  only  wonder  that 
fires  are  not  of  more  frequent  occurrence  in  theatres  where 
gas  is  employed.  When  incandescent  lamps  are  used  in- 
stead of  gas-lights,  this  danger  is  entirely  obviated,  provided 
the  most  elementary  precautions  are  taken,  fcr  the  electric 
lamps  will  not  ignite  even  paper  or  muslin  merely  brought 
into  momentary  contact  with  them,  though  such  materials 
would  take  fire  in  the  course  of  time  if  they  were  wrapped 
round  the  lamps,  or  allowed  to  rest  upon  them  while 
incandescent. 

It  is  of  course  necessary  in  carrying  out  an  electric  light 
installation  in  a theatre,  as  in  a private  house  or  elsewhere, 
that  the  work  should  be  done  in  a proper  manner,  and  by 
men  who  understand  their  business;  for  if  the  work  were 


238  ELECTRICITY  IN  MODERN  LIFE 

carelessly  done,  heating  might  take  place,  owing  to  bad  con- 
tacts; or  if  the  positive  and  negative  mains  were  brought 
too  close  together  at  any  point,  an  arc  might  be  formed 
across  them.  A good  many  fires  were  caused  in  'this  way 
in  some  of  the  earlier  installations;  for  before  people  had 
become  generally  alive  to  the  fact  that  a badly  carried 
out  installation  might  be  a source  of  very  serious  danger 
in  this  direction,  unskilled  workmen  were  allowed  to  carry 
out  the  work  without  proper  supervision.  As  regards  the 
comfort  of  the  audience,  the  electric  light  also  possesses  a 
very  great  advantage  over  illumination  by  gas,  on  account 
of  its  comparatively  small  heating  effect. 

Any  of  my  readers  will  be  able  to  test  this  for  them- 
selves, if  they  have  not  already  done  so,  by  comparing  the 
atmosphere  toward  the  end  of  the  performance  at  an  elec-, 
trically  lighted  theatre  with  that  of  a theatre  lighted  by  gas. 

The  electric  light  also  lends  itself  much  more  readily 
than  gas  to  scenic  effects,  as  by  the  introduction  of  suitable 
resistances,  either  directly  into  the  lighting  circuit,  or  into 
the  exciting  circuit  of  the  dynamo,  the  intensity  of  the  light 
may  be  varied  by  imperceptible  steps  from  full  brilliancy  to 
complete  extinction. 

The  first  of  the  London  theatres  which  was  lighted  by 
electricity  was  the  Savoy,  which  was  then,  as  now,  under 
the  direction  of  M.  D’Oyley  Carte,  and  special  credit  is  due 
to  him  for  his  enterprise  in  introducing  the  light,  as  this 
was  the  first  time  that  an  incandescent  electric  lighting 
installation  was  carried  out  upon  any  considerable  scale. 

The  work  was  done  by  Messrs.  Siemens  in'the  year  1881, 
and  the  lighting,  which  has  remained  under  their  charge 
ever  since,  has  been  thoroughly  satisfactory  in  every  way 
from  the  time  it  was  first  introduced.  Since  then  the  system 


ELECTRIC  LIGHTING 


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of  incandescent  lighting  has  been  introduced  into  a good 
many  other  theatres — the  Criterion,  the  Prince  of  Wales’s, 
Terry’s  Theatre,  the  Adelphi,  and  the  recently-built  Lyric 
and  Shaftsbury  Theatres  being  now  lighted  by  incandescent 
electric  lamps. 

In  all  modern  installations  of  the  electric  light  in  the 
interior  of  buildings,  safety-fuses  are  inserted  wherever  a 
branch  wire  leaves  the  mains,  and  in  some  cases  they  are 
attached  to  each  lamp,  or  group  of  lamps.  They  consist 


Fig.  74. 


simply  of  a short  wire  which  will  fuse  before  the  current 
has  become  great  enough  to  cause  danger  to  the  lamp,  and 
will  thus  cut  the  lamp,  or  group  of  lamps,  out  of  the  circuit. 
Similar  safety -fuses  are  placed  wherever  an  increase  of  the 
current  beyond  a certain  amount  would  be  likely  to  cause 
danger  of  fire,  and  large  magnetic  cut-outs  are  often  attached 
to  the  mains  as  they  leave  the  dynamos,  and  adjusted  so 
that  they  will  cut  oft*  the  current  as  soon  as  it  rises  beyond 

a fixed  maximum  value.  Fig.  74  illustrates  a safety-fuse, 

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ELECTRICITY  IN  MODERN  LIFE 


and  the  manner  of  attaching  it  to  a lamp,  or  group  of  lamps, 
suspended  from  the  ceiling  in  the  room  of  a house. 

Private  Installations. — As  the  number  of  central  stations 
increases,  private  installations,  as  far  as  the  larger  towns  are 
concerned,  will  probably  become  gradually  rarer;  but  their 
use  will  most  likely  extend  still  more  than  it  has  already 
done  for  the  purpose  of  lighting  isolated  country  houses, 
in  place  of  employing  private  gas  plants,  the  presence  of 
which  in  the  neighborhood  of  a house  is  exceedingly  objec- 
tionable, owing  to  the  injurious  and  foul-smelling  gases 
contained  in  coal-gas  as  it  comes  from  the  retorts,  and  from 
which  it  has  to  be  purified  as  far  as  possible  before  it  is 
used.  Where  water-power  is  available,  electric  lighting, 
independently  of  its  other  advantages,  is  the  most  econom- 
ical system  which  can  be  adopted,  but  where  this  is  not  to 
be  obtained,  a gas  engine  is  probably  the  most  convenient 
motive-power  to  employ.  In  a place  where  coal-gas  is 
already  available  this  may  be  employed  for  driving  the  gas 
engine,  but  even  when  this  is  not  the  case  a gas  engine  may 
still  be  employed,  for  engines  of  this  kind  are  now  made 
which  manufacture  their  own  gas  from  petroleum. 

Fig.  75  shows  the  arrangement  of  a small  private  instal- 
lation of  this  kind  carried  out  on  the  accumulator  system, 
the  dynamo  being  driven  by  a gas  engine.  The  lamps  are 
connected  across  the  negative  and  positive  mains,  as  shown 
in  Fig.  76,  which  illustrates  the  general  arrangement  of  the 
connections  in  a private  installation  in  which  accumulators 
are  employed.  The  switches  used  for  turning  the  dynamo 
current  directly  on  to  the  house  leads,  and  for  connecting 
these  and  the  dynamo  with  the  accumulators,  are  usually, 
for  the  sake  of  convenience,  fixed  on  a single  board,  as 
shown  in  the  illustration.  When  the  current  from  the  ac- 


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cumulators  is  in  use,  they  must  not  be  allowed  to  discharge 
at  more  than  a certain  rate,  as  if  this  were  exceeded  they 
would  be  damaged.  In  order  to  prevent  this  from  taking 
place  unperceived,  an  automatic  current-alarm,  connected 
with  a bell,  is  employed,  as  shown  in  the  centre  of  the  illus- 
tration. The  current-alarm  consists  of  a coil  of  wire,  with 
a soft-iron  core  suspended  in  its  centre,  and  kept  in  position 
by  means  of  a spring.  As  the  strength  of  the  current 
increases,  the  iron  is  drawn  further  into  the  coil,  until, 
when  a certain  point  is  reached,  the  bell  is  started  and  con- 
tinues ringing  until  the  discharge  current  is  lowered  to  the 
proper  amount. 

Accumulators  are  almost  invariably  employed  in  private 
installations,  for  if  they  were  not  used  the  engine  would 
always  have  to  be  kept  running  as  long  as  the  light  was 
required,  while,  when  they  are  employed,  they  can  usually 
be  charged  sufficiently  to  supply  all  the  current  required,  by 
running  the  engine  two  or  three  days  a week.  It  would  be 
impossible,  moreover,  to  get  a satisfactory  light  without  the 
use  of  accumulators  from  a dynamo  driven  by  any  form  of 
gas  engine  at  present  in  use,  as  these  engines  cannot  be 
made  to  run  with  the  same  regularity  as  steam  engines, 
and  the  result  would  be  that  the  light  would  fluctuate 
at  every  revolution  of  the  engine,  which  would  of  course 
be  exceedingly  disagreeable. 

Train  Lighting. — Another  very  useful  application  of 
accumulators  is  to  the  electric  lighting  of  trains,  which 
has  been  carried  out  with  the  greatest  success  during  the 
last  few  years  on  the  Great  Northern,  and  the  London, 
Brighton  and  South  Coast  Eailways. 

The  accumulators  are  made  by  the  Electrical  Power 
Storage  Company,  and  are  of  the  same  character  as  the 


ELECTRIC  LIGHTING 


243 


one  previously  described,  except  that  the  cells  are  made 
of  such  a shape  as  to  permit  of  their  being  conveniently 
stowed  away  in  boxes  under  the  seats  of  the  carriages. 

The  South  Eastern  Eailway  Company  also  has  quite 
recently  fitted  electric  reading-lamps  to  the  carriages  on 
the  main-line  trains.  The  lamps,  which  are  of  five-candle 
power,  are  contained  in  small  boxes  placed  just  under  the 
racks. 

The  light  is  obtained  by  introducing  a penny  into  a slot 
at  the  top  of  one  of  these  boxes,  and  then  pressing  a knob, 
and  it  will  last  for  half  an  hour,  at  the  end  of  which  time 
it  extinguishes  itself  automatically.  The  light  can  be  ob- 
tained for  as  long  a time  as  is  required  by  placing  a penny 
in  the  box  every  half  hour,  and  it  can  be  extinguished 
at  any  moment  by  pressing  a second  button. 

If  the  instrument  is  out  of  order,  or  if  a coin  other  than 
a penny  is  put  into  the  slot,  the  coin  drops  right  through, 
and  can  be  recovered. 

Portable  Electric  Lamps, — It  is  evident  that  the  introduc- 
tion of  incandescent  electric  lamps  would  be  of  the  greatest 
value  for  the  use  of  divers,  as,  owing  to  there  being  no  com- 
bustion, a supply  of  air  is  not  required;  and  also  for  use 
in  coal-mines  containing  explosive  gases.  In  such  cases  as 
these  it  would  not  always  be  convenient  to  have  the  lamps 
attached  to  long  wires  leading  to  the  source  of  current. 
Primary  batteries  might,  of  course,  be  used,  and  indeed 
they  have  been  used,  for  portable  lamps;  but,  in  addition 
to  the  expense  involved  in  their  being  lighted  in  this  way, 
a primary  battery,  to  give  a light  for  any  length  of  time, 
would  be  too  bulky  to  be  conveniently  carried  about.  Both 
these  defects  are  got  over  by  the  use  of  accumulators,  and 
a portable  lamp  of  'this  kind,  manufactured  by  the  Edison- 


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ELECTRICITY  IN  MODERN  LIFE 


Swan  United  Electric  Light  Company,  is  shown  in  Fig.  77. 
The  lamp  is  energized  by  a four-cell  accumulator,  shown 
in  Fig.  78. 

This  accumulator  is  contained  in  a strong  teak  box, 
A,  Fig.  77,  strengthened  with  metal  bands,  BB.  A small 
incandescent  lamp  is  attached  to  the  side  of  the  case,  and 
protected  by  a strong  glass  cover,  C,  with  a cross-bar,  G, 
and  a hinged  lever  secured  by  a safety-nut,  F,  and  provided 


Fig.  77. 


Fig.  78. 


with  a swivel  handle,  D.  The  lamp  can  only  be  opened  by 
means  of  a key,  so  that  it  cannot  be  got  at  by  the  miners. 
In  some  lamps  of  this  kind  which  have  recently  been  con- 
structed, a small  lever  is  provided  which  maintains  the 
continuity  of  the  circuit  as  long  as  it  is  pressed  down  by 
the  glass  cover,  C,  but  breaks  the  circuit  when  allowed 
to  rise,  which  it  would  at  once  do  if  the  outer  glass  cover 
were  accidentally  broken.  The  object  of  this  arrangement 


ELECTRIC  LIGHTING 


245 


is  to  prevent  a miner  from  continuing  to  use  a lamp  of 
which  the  outer  covering  has  been  broken,  as  if  this  were 
done  the  glass  globe  of  the  lamp,  being  of  very  much  thin- 
ner glass  than  the  outer  covering,  would  be  very  likely  to 
get  broken,  and  although  the  lamp  would  be  extinguished 
almost  immediately  by  the  fibre  burning  away,  there  might 
be  just  time  for  it  to  ignite  the  explosive  gas  in  the  mine. 


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CHAPTER  XVI 

ELECTRO-MOTORS  AND  THEIR  USES 

An  electro-motor  is  really  nothing  but  a dynamo  work- 
ing backward — that  is  to  say,  one  which,  instead  of 
being  driven  by  the  application  of  external  power, 
and  thereby  transforming  the  energy  supplied  by  a steam 
engine  or  other  prime  motor  into  the  form  of  electrical 
energy,  is  supplied  with  electrical  energy  by  means  of  an 
electric  current,  which  sets  the  motor  in  motion,  and  trans- 


Fig.  79. 

forms  the  electrical  energy  into  mechanical  energy.  Fig.  79 
illustrates  a motor  made  by  Messrs.  Immisch  & Co.,  one  of 
the  few  firms  which  have  devoted  themselves  to  the  con- 


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struction  and  improvement  of  the  electro-motor,  and  whose 
motors  have  already  obtained  a world-wide  reputation  for 
high  efficiency  and  good  workmanship. 

Another  type  of  motor,  manufactured  by  the  Electrical 
Power  Storage  Company,  is  shown  in  Fig.  80. 

The  reversibility  of  the  dynamo,  enabling  it  to  act  as  a 
motor  when  supplied  with  electric  current,  was  first  made 
known  by  M.  Hippolyte  Fontaine  at  the  Vienna  Inter- 
national Exhibition  of  1873.  According  to  M.  Figuier,  the 
discovery  was  purely  accidental. 

Figuier’s  account  is  that  the  Gramme  Company  had  two 
machines  exhibited  at  the  Exhibition,  and  one  day  while 
one  of  these  machines  was  in  motion,  and  the  other  one  was 
standing  still,  a workman,  seeing  some  cable  ends  lying  loose 
upon  the  floor,  fancied  that  they  belonged  to  the  machine 
at  rest,  and  placed  them  in  its  terminals,  w’hen,  to  the 
astonishment  of  everybody,  the  armature  of  the  machine 
began  to  rotate,  being  driven  by  the  current  from  the  other 
machine.  Prior  to  this  a great  many  attempts  had  been 
made  to  construct  electric  engines,  or  motors  set  in  motion 
by  means  of  an  electric  current,  but  none  of  them  was  of 
any  practical  use,  and  they  were,  in  fact,  nothing  more  than 
scientific  toys.  Any  continuous  current  dynamo  can  be 
used  as  an  electro-motor;  but  in  the  construction  of  electro- 
motors it  is  much  more  important  to  make  the  weight  as 
small  as  possible  than  in  the  case  of  dynamos;  and  there  are 
some  other  points  which  are  of  greater  practical  importance 
in  the  case  of  electro-motors  than  in  the  case  of  dynamos, 
so  that,  although  the  principles  of  construction  are  the  same 
in  each  case,  it  is  not  very  often  that  machines  constructed 
for  producing  current  are  actually  employed  as  electro- 
motors. 


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ELECTRICITY  IN  MODERN  LIFE 


Electric  Railioays. — One  exceedingly  important  applica- 
tion of  the  electro-motor  is  its  employment  for  the  purpose 
of  traction.  For  some  time  past,  experiments  have  been 
in  progress  with  the  view  of  adopting  electric  traction  on 
the  underground  railways  in  London,  in  order  to  get  rid 
of  the  contamination  of  the  atmosphere  by  the  smoke 
and  other  products  of  combustion  from  the  locomotives, 
which  now  make  the  line  so  unpleasant  to  travel  upon. 
Electric  traction,  however,  has  not  yet  been  practically 
employed  for  heavy  railways,  though  it  has  been  used  to 
a considerable  extent  for  light  railways,  or,  as  we  call  them 
in  this  country,  tramways. 

The  electric  propulsion  of  cars  on  tramway  lines  can  be 
eflEected  in  two  distinct  ways.  One  is  to  place  accumulators 
on  the  car,  these  accumulators  being  charged  at  fixed  sta- 
tions, usually  at  one  or  both  of  the  termini.  The  principal 
disadvantage  of  the  accumulator  system  is  the  great  weight 
of  the  accumulators,  which  have  of  course  to  be  carried  by 
the  cars;  and  it  also  has  the  disadvantage  of  the  additional 
loss  incurred  in  two  transformations  of  energy,  as  in  the 
accumulator  system  the  energy  of  the  prime  motor  must  first 
be  transformed  into  electrical  energy,  and  then  into  chemical 
energy,  which  is  stored  up  in  the  battery,  from  which  it  is 
reproduced  in  the  form  of  electrical  energy,  and  then  again 
converted  into  mechanical  energy  in  the  motor.  The  advan- 
tages are  that  each  car  is  independent  of  every  other,  and 
that  no  fixed  conductors  are  required  along  the  line. 

The  accumulators  used  in  driving  cars  on  this  system 
are,  as  in  the  case  of  train-lighting,  stored  under  the  seats, 
and  in  any  case  the  electro-motors  are  usually  placed  under 
the  floor  of  the  car. 

The  other  method  of  driving  cars  electrically  is  to  em- 


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ploy  a fixed  source  of  energy,  and  to  transmit  the  current 
to  the  car  by  means  of  a conductor  and  sliding  contacts. 
Mr.  Gisbert  Kapp,  in  his  work  on  the  “Electrical  Trans- 
mission of  Energy,”  classifies  the  electric  railways  worked 
on  the  conductor  system  into  four  divisions,  according  to 
the  manner  in  which  the  current  is  conveyed  to  and  from  the 
car.  In  the  first  class  the  rails  are  insulated  from  the  ground, 
and  the  separate  rails  being  placed  in  electrical  communica- 
tion by  means  of  connecting  pieces,  they  are  employed  as 
conductors,  one  conveying  the  outflowing  and  the  other  the 
return  current.  The  car- wheels  in  this  system  have  to  be 
insulated  from  their  axles. 

A short  tramway  of  this  kind  has  been  erected  by  Mr. 
Volk  on  the  beach  at  Brighton,  and  another  one  is  in  use 
in  Berlin. 

The  second  class  consists  of  those  in  which  a separate 
conductor  is  used  for  the  outflowing  current,  while  the  re- 
turn current  is  carried  by  both  rails.  The  rails  need  not 
be  insulated,  but  must  be  in  electrical  communication 
throughout  by  means  of  special  connecting  pieces  at  the 
joints.  The  Bessborough  and  Newry  Electric  Eailway  is 
a good  example  of  this  class;  it  is  three  miles  in  length, 
and  the  electric  current  is  supplied  by  two  Edison-Hopkin- 
son  dynamos  driven  by  a large  turbine  placed  at  a station 
at  about  the  middle  of  the  line,  where  ample  water-power 
is  available. 

Other  examples  of'  this  kind  are  given  by  the  railways 
at  Portrush  and  Blackpool. 

In  the  third  class  separate  conductors  are  used  for  the 
outflowing  and  the  return  current.  These  are  carried  over- 
head on  poles,  and  usually  consist  of  iron  or  copper  tubes. 
A line  of  this  kind  is  now  in  use  between  Frankfort  and 


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ELECTRICITY  IN  MODERN  LIFE 


Offenbach  on  the  Maine.  A portion  of  it  is  shown  in  Fig. 
81.  The  conductors  consist  of  tubes  of  wrought-iron,  of  one 
inch  internal  diameter,  and  one  and  one-fifth  inches  external 
diameter,  suspended,  by  means  of  iron  wire  ropes,  from 
ordinary  telegraph  poles.  A slot  is  cut  out  along  the  whole 
length  of  each  tube,  and  the  current  is  conveyed  to  and 
from  the  car  by  means  of  wires  attached  to  small  cylinders 
of  cast-iron,  which  slide  within  the  tubes.  The  same  system 
is  in  use  in  Berlin,  Vienna,  and  other  places. 

In  the  fourth  class  separate  conductors  are  used  for  the 
outflowing  and  return  current,  and  these  are  attached  to 
poles,  and  arranged  so  as  to  form  a single  line  on  which 
suspended  trucks  run.  This  is  known  as  the  telepherage 
system,  and  was  devised  by  Professors  Ayrton,  Perry,  and 
Fleeming  Jenkin  for  carrying  light  loads  over  hilly  or 
mountainous  country.  The  first  line  of  this  kind  was  con- 
structed at  Glynde,  in  Sussex,  and  has  been  a complete 
success.  Pig.  82  shows  a similar  line  which  has  been  con- 
structed in  America  by  the  Sprague  Electric  Eailway  and 
Motor  Company,  for  the  purpose  of  carrying  ore  from  a mine 
on  a mountain  side  to  a railway  at  the  base.  The  road,  or 
overhead  track,  consists  of  two  stationary  steel  cables,  sus- 
pended one  above  the  other,  between  posts  of  wood  or 
metal,  fifty  feet  or  more  apart,  and  at  such  a height  from  the 
ground  as  not  to  interfere  with  the  surface  traffic.  The  cars 
run  on  wheels,  and  are  suspended  between  the  upper  and 
lower  cables,  the  upper  cables  carrying  most  of  the  weight. 
Each  car  contains  an  electro-motor,  which  is  supplied  with 
current  by  contact  of  the  wheels  with  the  cables. 

Several  attempts  have  been  made  to  apply  electricity  to 
ordinary  street  locomotion.  One  of  the  first  of  these  was  an 
electric  tricycle  designed  by  Professors  Ayrton  and  Perry. 


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Some  dog-carts  driven  by  electricity  have  also  recently  been 
constructed  by  Messrs.  Immisch  & Co.  One  of  these  was 
made  for  the  Sultan  of  Turkey  in  September,  1888,  and  he 
appears  to  have  been  so  pleased  with  it  that  he  has  ordered 
another  one  to  be  sent  out.  This  is  of  an  improved  pattern, 
and  is  shown  in  Fig.  83.  The  power  is  stored  in  twenty- 
four  small  accumulators,  which  weigh  about  seven  hundred- 
weight, and  contain  a charge  sufficient  to  propel  the  vehicle  at 
a speed  of  ten  miles  an  hour  for  about  five  hours.  The  cart 
is  driven  by  a one-horse-power  Immisch  motor.  The  total 
weight  of  the  carriage  and  accumulators  is  about  eleven 
hundredweight. 

These  carts  are  only  suitable  for  use  on  the  level,  and 
on  good  roads,  as  the  wheels  have  not  got  sufficient  grip 
to  carry  the  cart  up  any  considerable  incline,  and  this  is  one 
of  the  chief  difficulties  in  propelling  any  carriages,  other 
than  extremely  heavy  ones,  such  as  traction  engines,  either 
by  electricity  or  by  steam  power. 

An  ’ electric  omnibus  has  also  recently  been  tried  in 
London,  but  I believe  it  was  only  run  at  night,  which  was 
certainly  a most  desirable  precaution,  as,  owing  to  the 
weight  of  the  accumulators,  electrically  propelled  vehicles 
are  difficult  to  stop  suddenly,  and  on  one  occasion  when  it 
was  being  run  at  night  in  Oxford  Street,  a hansom  cab 
dashed  out  of  a side  street  in  front  of  it,  and  the  driver, 
unable  to  stop  in  time,  stated  afterward  that  there  were 
three  alternatives  open  to  him — viz.,  either  to  run  into  the 
lamp-post,  the  hansom,  or  the  nearest  house.  He  chose 
the  former,  breaking  the  lamp-post  off  near  the  ground,  and 
planting  the  car  on  the  top  of  it.  The  passengers  inside 
were  of  course  covered  with  the  acids  from  the  cells,  and 
one  of  them  foolishly  striking  a light,  ignited  the  gas  from 


252 


ELECTRICITY  IN  MODERN  LIFE 


the  broken  lamp-post,  so  that  had  they  not  shortly  been 
released  from  their  perilous  position  they  would  all  have 
been  burned. 

Another  interesting  example  of  the  use  of  the  electro- 
motor for  the  purpose  of  traction  is  its  application,  as  far 
back  as  1879,  to  plowing  fields  in  the  neighborhood  of  the 
beetroot  factory  at  Sermaize.  The  manufacture  of  beet 
sugar  is  only  carried  on  during  a small  portion  of  the  year, 
so  that  for  the  rest  of  the  time  the  machinery  remains  idle, 
and  it  occurred  to  the  proprietors  that  it  would  be  advan- 
tageous to  use  the  steam  engine  during  this  slack  time  for 
plowing  the  fields  in  the  neighborhood.  The  experiment 
was  perfectly  successful.  The  current  was  generated  at  the 
factory  by  means  of  a Gramme  dynamo  driven  by  the  steam 
engine,  and  the  plowing  arrangement  was  similar  to  that 
adopted  in  steam  plowing,  the  plow  being  drawn  backward 
and  forward  across  the  field  by  a steel  wire  rope  coiled  and 
uncoiled  alternately  from  drums  carried  on  trolleys  placed 
at  opposite  sides  of  the  field,  and  each  provided  with  a 
Gramme  dynamo  used  as  a motor. 

Electric  Launches, — The  electrical  method  of  propulsion 
is  extremely  well  suited  for  small  launches,  in  the  place  of 
steam,  and  a large  number  are  now  in  use.  Fig.  84  shows 
the  general  appearance  of  an  electric  launch  as  manufactured 
by  the  Electrical  Power  Storage  Company.  The  sectional 
diagram,  Fig.  85,  shows  the  position  of  the  motor  under 
the  deck  of  the  launch,  and  of  the  accumulators,  which 
are  shown  extending  from  the  motor  to  near  the  bow  of  the 
vessel.  The  great  advantages  of  this  method  of  propulsion 
are  the  complete  absence  of  smoke  and  dirt,  and  the  in- 
creased room,  owing  to  the  whole  of  the  machinery  being 
placed  below  the  deck.  The  chief  difficulty  attending  the 


ELECTRO-MOTORS  AND  THEIR  USES 


263 


254 


ELECTRICITY  IN  MODERN  LIFE 


use  of  the  electro-motors  for  propelling  steam  launches  is 
that  they  cannot  run  to  any  great  distance  froni  the  charging 
station. 

Messrs.  Immisch  & Co.,  who  have  constructed  a number 
of  these  launches,  have  endeavored  to  remedy  this  want 
on  the  river  Thames  by  the  construction  of  a number  of 
stations  at  intervals  for  charging  accumulators,  so  that  a 
launch  on  arriving  at  one  of  these  stations  can,  if  its  accu- 
mulators have  run  down,  have  them  exchanged  for  fresh 
ones  and  proceed  upon  its  journey. 

Other  Applications  of  Electro ^ Motors. — Electro-motors  are 
now  coming  into  extensive  use  in  mountainous  countries, 
as,  for  example,  in  Switzerland,  for  driving  machinery  by 
means  of  water-power,  at  distances  which  sometimes  extend 
to  several  miles.  In  America,  where  electric  lighting  from 
central  stations  is  much  more  general  than  in  this  country, 
electro-motors  are  very  largely  used  for  driving  machinery 
in  small  workshops,  where  the  power  required  would  not 
be  sufficient  to  make  it  worth  while  to  use  a steam  engine. 
These  motors  are  used  for  driving  printing  presses,  tailors’ 
and  shoemakers’  sewing  machines,  watchmakers’  lathes,  and 
similar  apparatus;  and  there  is  no  doubt  that,  as  the  system 
of  supplying  electric  current  from  central  stations  extends 
in  London  and  other  English  towns,  electro-motors  will  be 
more  and  more  employed  for  similar  purposes  in  this 
country.  One  of.  the  great  advantages  of  the  electro-motor 
for  purposes  such  as  these  is  that  it  can  be  fixed  just  where 
it  is  required,  and  used  to  drive  a machine,  without  the 
intervention  of  belts,  driving  pulleys,  and  shafting.  This 
is  very  well  illustrated  in  Fig.  86,  which  shows  an  electro- 
motor driving  one  of  the  fans  now  so  extensively  used  for 
ventilating  ships,  factories,  mines,  etc.  For  driving  venti- 


ELECTRO-MOTORS  AND  THEIR  USES  ■ 


255 


lators  and  other  machinery  in  mines  the  electro-motor  is 
especially  valuable,  as  it  does  away  with  the  driving  rods 
and  other  moving  gear,  which  has  always  been  a source  of 
trouble  in  the  shaft  of  a mine,  replacing  it  by  a simple 


Fig.  86. 

fixed  cable.  With  regard  to  the  applications  of  electro- 
motors for  use  in  private  houses,  where  the  electric  current 
is  supplied  from  central  stations  for  lighting  purposes,  such 
of  my  readers  as  may  be  amateur  mechanics  will  easily  per- 


256 


ELECTRICITY  IN  MODERN  LIFE 


ceive  what  an  advantage  it  would  be  to  be  able  to  drive 
their  lathes  or  other  machinery  by  means  of  a small  motor 

which  could  be  set  in  action  in  a mo- 
ment by  simply  inserting  a pair  of 
contact  plugs  into  a shoe^  as  it  is 
called,  fixed  at  any  convenient  part 
of  the  room.  Fig.  87  shows  a shoe 
suitable  for  this  purpose,  or  for  use 
with  an  electric  reading-lamp.  Some 
of  my  lady  readers  would  probably 
be  glad  to  work  their  sewing  ma- 
chines in  a similar  manner,  by  means 
of  a motor  which  can  be  fixed  di- 
rectly under  the  table  which  sup- 
ports the  machine,  and  which  will 
occupy  considerably- less  space  than  the  treadle  arrange- 
ment generally  employed. 


Fiii.  87. 


ELECTBO--METALLUBQY 


CHAPTER  XYII 

ELECTRO-METALLURGY 

(PROPOSE  to  consider  under  this  head  the  electrical 
deposition  of  metals,  or,  as  it  is  now  called,  electro- 
plating, and  the  application  of  electricity  to  the  puri- 
fication of  metals  and  the  reduction  of  metallic  ores,  together 
with  the  recently -invented  process  of  electric  welding. 

One  of  the  first  experiments  tried  by  every  schoolboy 
who  has  been  allowed  to  amuse  himself  in  his  holidays  by 
constructing  and  experimenting  with  galvanic  batteries,  is 
to  copy  medals  or  coins  by  taking  models  of  them  in  some 
such  substance  as  plaster  of  Paris,  then  making  the  surface 
of  the  model  a conductor  of  electricity  by  rubbing  it  over 
with  black-lead,  and  finally  electro-plating  it  with  copper, 
by  attaching  it,  by  means  of  a wire,  to  the  negative  pole  of 
a battery,  and  suspending  it  in  a vessel  containing  a solu- 
tion of  sulphate  of  copper  in  which  is  suspended  a plate  of 
copper,  connected  by  means  of  a wire  to  the  positive  pole 
of  the  battery. 

In  the  year  1801  Wollaston  discovered  that  if  a piece 
of  silver  in  connection  with  a more  positive  metal  were  im- 
mersed in  a solution  of  copper,  the  silver  became  coated 
over  with  a layer  of  copper  sufficiently  coherent  to  stand 
the  operation  of  burnishing.  Two  years  later  Oruickshank 


258 


ELECTRICITY  IN  MODERN  LIFE 


observed  that  when  a current  from  a galvanic  battery  was 
passed,  by  means  of  silver  wires,  through  solutions  of  vari- 
ous salts  of  lead,  copper,  and  silver,  the  metals  attached 
themselves  to  the  wire  connected  to  the  zinc  end  of  the 
battery;  and  in  the  year  1805  Brugnatelli  made  the  first 
practical  application  of  electro-plating  of  which  we  have 
any  record  by  gilding  two  silver  medals,  by  attaching  them 
to  the  negative  pole  of  a battery,  and  suspending  them  in 
a saturated  solution  of  a salt  of  gold. 

Electro-plating,  as  a practical  art,  may  however  be  con- 
sidered as  deriving  its  origin  from  the  work  of  Professor 
Jacobi  of  St.  Petersburg,  and  of  T.  Spencer  of  Liverpool, 
in  the  year  1839.  Jacobi’s  galvano-plastic  process,  as  he 
called  it,  enabled  him  to  convert  any  line,  however  fine, 
of  an  engraving  on  copper,  into  a relief,  by  an  electro- 
plating process  which  he  describes  as  being  applicable  to 
copper-plate  engraving,  copying  medals,  producing  stereo- 
type  plates,  copper-plating  plaster  ornaments,  and  the  man- 
ufacture of  calico  printing  blocks  and  patterns  for  paper 
hangings. 

The  first  patents  in  this  country  and  in  France  were 
taken  out  by  Messrs.  Elkington,  of  Birmingham,  who  still 
occupy  the  foremost  position  in  the  electro-plating  industry 
in  this  country. 

The  earlier  electro-plating  work  was  of  course  carried 
out  by  means  of  primary  batteries;  but  these  are  no  longer 
used  for  the  purpose,  except  for  operations  on  a very  small 
scale — such,  for  example,  as  those  of  the  schoolboy  to  whom 
I have  referred— and  the  electric  current  required  for  the 
purpose  is  now  always  obtained  from  dynamos.  The  dyna- 
mos employed  for  the  transmission  of  electric  energy  and 
for  producing  electric  lighting  currents  would  be  quite  un- 


ELECTRO-MET  ALL  URG  Y 


259 


suitable  for  use  in  electro-plating,  for  the  quantity  of  metal 
deposited  in  the  bath  depends  only  on  the  strength  of  the 
current,  and  not  upon  its  electro-motive  force,  so  that  it  is 
only  necessary  to  obtain  an  electro-motive  force  sufficient 
to  drive  the  current  through  the  bath  of  liquid  in  which 
the  objects  to  be  plated  are  immersed.  An  electro-motive 
force  of  four  or  five  volts  is  usually  amply  sufficient  for  this 
purpose;  and  if  it  is  much  higher  than  is  required,  not  only 
is  there  a useless  waste  of  energy,  but  it  is  found  that  the 
metallic  deposits  become  uneven  and  wanting  in  coherence. 

The  dynamos  to  supply  current  for  electro-plating  must 
therefore  give  a large  current  at  low  pressure,  and  there- 
fore they  must  have  a very  small  internal  resistance,  which 
means  that  the  coils  must  be  made  of  thick  wire,  and  there- 
fore comparatively  short.  Continuous  current  dynamos  are 
of  course  the  only  ones  that  can  be  employed  for  electro- 
plating, and  the  method  of  exciting  them  must  be  such  that 
there  is  no  danger  of  the  current  becoming  reversed,  as  the 
result  of  this  would  be  to  remove  the  metal  which  had 
already  been  deposited  upon  the  object  to  be  plated. 

One  of  the  most  important  and  best  known  electro- 
plating operations  consists  in  the  deposition  of  gold  and 
silver  on  various  less  expensive  metals.  Another  impor- 
tant application,  which  is  rapidly  becoming  a great  indus- 
try, consists  in  covering  readily  oxidizable  metals  like  iron 
with  a thin  layer  of  a more  durable  material,  such  as  nickel. 
This  process  is  largely  employed  for  trappings  of  harness, 
the  ironwork  of  carriages  and  cycles,  and  also  for  many 
articles  of  ordinary  daily  use. 

The  electro  deposition  of  iron,  first  carried  out  by  Jacobi 
and  Klein,  has  recently  found  an  important  application  at 
the  hands  of  Professor  Eoberts-Austin,  who  employed  it  for 


260 


ELECTRICITY  IN  MODERN  LIFE 


obtaining  the  dies  for  striking  the  medals  issued  on  the  oc- 
casion of  the  Queen’s  Jubilee.  The  medals  were  originally 
modelled  in  plaster,  and  the  casts  reproduced  by  the  electro 
deposition  of  copper;  and  finally  these  copper  dies  were 
plated  with  coherent  layers  of  iron,  nearly  a tenth  of  an 
inch  in  thickness,  and  hard  enough  to  be  used  for  stamp- 
ing. The  greatest  drawback  to  this  very  interesting  process 
is  that  the  operation  of  obtaining  a layer  of  this  kind,  suffi- 
ciently hard  to  be  used  for  stamping,  occupies  from  three 
to  five  weeks. 

In  Chapter  X.  I alluded  to  the  fact  that  copper  wire 
of  great  tensile  strength  and  very  low  electrical  resistance 
is  now  being  produced  at  a lower  price  than  used  for- 
merly to  be  paid  for  ordinary  commercial  copper.  This 
is  effected  by  means  of  a process  designed  by  Mr.  Elmore, 
and  which  is  now  being  carried  out  at  a factory  erected 
for  the  purpose  at  Cockermoath. 

The  process,  which  is  not  only  applicable  to  the  pro- 
duction of  telegraph  wires,  but  also  to  the  manufacture  of 
copper  steam-pipes,  suitable  for  boilers  and  other  purposes, 
of  great  strength  and  homogeneity,  is  known  as  the  electro 
hurnishing  process^  and  consists  in  the  electro  deposition  of 
copper  upon  a mandril  immersed  in  the  copper  bath,  and 
maintained  in  continuous  rotation. 

The  copper  as  it  is  deposited  is  compressed  into  a firm 
homogeneous  mass  by  means  of  a burnisher,  which  always 
presses  against  the  mandril,  and  traverses  continually  up 
and  down  it  as  the  latter  rotates. 

Tubes  of  a very  large  size  can  be  made  directly  in  this 
manner,  and  in  order  to  obtain  a telegraph  wire  from  one 
of  these  tubes  a helical  cut  is  made,  by  means  of  machinery 
specially  constructed  for  the  purpose,  starting  from  one  end 


ELECTRO-METALL  URG  Y 


261 


of  the  cylinder  and  passing  round  it  in  a helix  until  it 
reaches  the  bottom.  A helical  strip  of  copper  of  square 
section  is  thus  obtained,  and  this  is  drawn  through  a series 
of  circular  holes  gradually  diminishing  in  size,  cut  in  steel 
plates,  until  the  strip  has  been  drawn  out  into  wire  of  the 
required  gauge.  The  latter  part  of  the  operation  is  exactly 
similar  to  the  ordinary  process  of  wire-drawing. 

In  the  year  1871  Elkington  first  proposed  to  precipitate 
copper  electrolytically  from  the  fused  sulphate  of  copper 
and  iron  which  the  copper-smelter  designates  by  the  term 
regulus.  Thin  copper  plates  were  arranged  to  receive  the 
copper  as  it  was  deposited,  while  the  other  metals  present, 
including  gold  and  silver,  fell  to  the  bottom  of  the  solution. 

Electricity  has  also  been  largely  employed  for  obtaining 
pure  copper  from  the  impure  form  known  as  “blister  cop- 
per’’ or  “blade  copper,”  the  impure  metal  being  attached 
to  the  positive  terminal  of  the  dynamo,  and  immersed  in  a 
bath  of  sulphate  of  copper,  while  the  pure  metal  is  deposited 
on  a thin  strip  of  copper  attached  to  the  negative  terminal  of 
the  dynamo.  This  process  is  now  so  extensively  used  that 
large  dynamos  have  been  specially  constructed,  which,  with 
an  expenditure  of  100  horse-power,  will  produce  eighteen 
tons  of  pure  copper  per  week. 

It  was  suggested  by  the  late  Sir  William  Siemens  that 
the  exceedingly  high  temperature  of  the  electric  arc  might 
be  advantageously  utilized  in  the  fusion  of  metals  with  high 
melting  points,  and  he  actually  constructed  an  electrical  fur- 
pace  in  which  ninety-six  ounces  of  platinum  could  be  melted 
in  ten  minutes. 

His  experiments  were  unfortunately  interrupted  by  his 
untimely  death,  but  the  method  has  been  recently  developed 
and  carried  out  on  a very  large  scale  by  Messrs.  Cowles,  for 


262 


ELECTRICITY  IN  MODERN  LIFE 


the  purpose  of  isolating  aluminium  from  corundum,  and 
alloying  it  immediately  with  copper  or  iron,  in  order  to 
produce  the  aluminium  alloys  which  are  now  so  exten- 
sively employed  for  various  purposes.  .The  adaptability 
of  the  electric  arc  for  the  production  of  aluminium  alloys 
was,  like  many  other  important  discoveries,  made  acci- 
dentally, while  the  inventors  were  engaged  upon  a re- 
search directed  to  a totally  different  object.  It  appears 
that  the  two  brothers,  E.  H.  & A.  H.  Cowles,  went  over 
to  South  America  some  time  ago  to  develop  a zinc  mine 
in  which  their  father  had  invested  a considerable  amount 
of  capital.  The  ore  was  found  to  be  extremely  rich,  not 
only  in  zinc,  but  also  in  silver;  it  was,  however,  so  re- 
fractory that  it  could  not  be  reduced  in  the  furnaces 
which  were  available. 

Some  of  the  ore  was  then  sent  to  Ohio  to  be  reduced 
in  a more  powerful  furnace,  but  even  this  failed  to  reduce 
it;  and  it  therefore  appeared  at  first  sight  as  if  the  mine 
would  have  to  be  abandoned,  but,  fortunately,  one  of  the 
brothers  was  an  electrician  and  the  other  a chemist,  and 
the  former  suggested  that  the  high  temperature  of  the  elec- 
tric arc  might  possibly  be  turned  to  account  to  extricate 
them  from  their  difficulty. 

They  immediately  set  to  work  experimenting  with  the 
object  of  testing  this  suggestion.  In  their  first  experiments 
they  filled  a pipe  of  fire-clay  with  a mixture  of  the  crushed 
ore  and  charcoal  powder,  placed  a bunch  of  electric  light 
carbons  at  each  end  of  it  to  act  as  electrodes,  and  closed 
up  the  ends.  A current  from  a small  dynamo  was  then 
sent  through  the  pipe,  and  after  a short  time  the  ore  was 
found  to  be  reduced,  but  the  pipe  also  was  partly  melted, 
which  was  a very  undesirable  result. 


Science^  p.  251 — Vol.  13 


library  ^ 

OF  THE 

Rcrv  c;  ILUHOIS 


I. 


ELECTRO-MET  ALL  URG  Y 


263 


The  melting  of  the  pipe  was  soon  found  to  be  due  to  the 
fact  that  the  charcoal  powder,  which  in  its  original  form  was 
a bad  conductor  of  electricity,  was  converted  by  the  high 
temperature  into  graphite,  which  is  a fairly  good  conductor. 
The  difficulty  was  overcome  at  the  suggestion  of  the  chem- 
ist, Mr.  A.  H.  Cowles,  by  the  very  simple  method  of  soaking 
the  charcoal  powder  in  lime  water,  and  drying  it  before  use. 

The  coating  of  lime  thus  obtained  prevented  electric  con- 
duction between  the  neighboring  particles  of  the  charcoal, 
and  thus  enabled  it  to  retain  its  insulating  properties,  even 
when  a portion  of  it  had  been  converted  into  graphite.  The 
inventors  very  soon  recognized  that  this  furnace  was  exactly 
what  was  required  for  the  reduction  of  the  oxides  of  alu- 
minium, and  experiments,  which  were  perfectly  successful, 
were  very  soon  made  upon  corundum  as  the  raw  material. 
At  the  works  which  have  now  been  erected,  a current  of 
5,000  amperes  is  supplied  at  an  electro -motive  force  of  sixty 
volts,  by  means  of  a single  dynamo  of  immense  size,  prob- 
ably the  largest  which  has  ever  been  made. 

The  heating  power  of  large  currents  has  also  been  util- 
ized by  Elihu  Thomson  in  the  United  States,  and  by  Ber- 
nardo in  Eussia,  for  the  purpose  of  welding  metals.  The 
Thomson  process,  which  is  chiefly  employed  for  uniting 
wires  and  other  pieces  of  metal  of  comparatively  small 
cross  section,  consists  in  simply  pressing  together  the  two 
pieces  to  be  united,  while  a large  current  is  passing,  when 
the  heat  developed  at  the  junction  is  found  to  be  sufficient 
to  soften  even  refractory  metals  so  much  that  they  can  be 
easily  united.  Brazing  can  also  be  successfully  effected 
by  putting  brass  on  the  joint  while  the  current  is  passing. 
In  a paper  read  before  the  American  Society  of  Arts  in 

1886  Thomson  suggested  that  the  method  would  be  of  great 

Science — Vol;  XIIT — 12 


264 


ELECTRICITY  IN  MODERN  LIFE 


value  for  making  the  long  lengths  of  pipes  for  boiler  coils, 
for  making  endless  bands  for  saws,  wheel  tires,  and  iron 
and  steel  links  for  chains;  and  he  also  considered  that 
there  would  be  a wide  scope  for  the  process  in  the  repair 


Fig.  88. 


of  pulleys  and  parts  of  machines,  for  which  it  was  exten- 
sively used  in  the  Thomson-Houston  factory.  Welds  made 
by  this  process  have  been  severely  tested,  and  in  every  case 
it  has  been  found  that  the  weld  was  quite  as  strong  as  the 
other  portions. 


ELECTRO-METALL  URG  Y 


265 


Bernardo’s  process  consists  in  making  the  metal  to  he 
welded  the  negative  pole,  the  positive  pole  being  a carbon 
rod.  This  process  has  been  employed  to  a considerable  ex- 
tent for  repairing  metal  plates  in  situ^  as,  for  example,  the 
plates  of  a boiler.  In  order  to  weld  together  two  pieces 
of  boiler-plate,  one  of  the  terminals  of  a dynamo  or  set  of 
accumulators  is  attached  to  the  plate,  and  the  other  to  a 
carbon  rod  an  inch  in  thickness,  held  in  a portable  insu- 
lating holder;  the  metal  is  then  touched  with  the  rod,  which 
is  immediately  withdrawn  from  a quarter  to  half  an  inch, 
thus  forming  an  arc,  as  shown  in  Fig.  88,  which  is  taken 
from  a photograph. 

The  metal  at  the  point  where  the  arc  is  formed  melts  im- 
mediately like  wax,  and  runs  perfectly  fluid.  When  looked 
at  through  the  dark  glass  employed  to  shade  the  eye  from 
the  glare  of  the  arc,  the  latter  appears  like  a blow-prpe 
flame,  and  is  manipulated  in  very  much  the  same  way. 

The  use  of  accumulators  makes  the  whole  apparatus 
easily  portable,  so  that  it  can  be  carried  to  the  place 
where  the  repair  is  required,  instead  of  the  plates  having 
to  be  taken  out  and  carried  to  a forge,  and  then  brought 
back  and  replaced. 


266 


ELECTRICITY  IN  MODERN  LIFE 


CHAPTER  XVIII 


ELECTRICITY  IN  WARFARE 


Electrical  torpedoes.— I mentioned  in  Chap- 
ter XI.  that  some  of  the  earliest  submarine  electric 
cables  were  constructed  for  the  purpose  of  exploding 
mines  from  a distance.  Since  that  time  submarine  mines 
or  torpedoes  have  been  invented,  and  brought  to  a very 
high  state  of  perfection. 

Torpedoes,  such  as  those  of  Whitehead  or  of  Brennan, 
which  can  be  propelled  through  the  water,  to  attack  a hos- 
tile vessel,  are  almost  all  worked  by  purely  mechanical 
means  without  the  aid  of  electricity,  and  therefore  do  not 
come  within  the  scope  of  this  volume. 

In  the  case  of  fixed  or  stationary  torpedoes  or  submarine 
mines,  however,  this  is  not  the  case,  as  these  are  almost  in- 
variably controlled  and  fired  by  means  of  electric  currents. 
The  earlier  submarine,  mines  were  fired  mechanically  on 
being  struck  by  a vessel  passing  over  them,  but  the  use 
of  mines  of  this  kind,  even  when  they  are  of  the  most  per- 
fect construction,  is  attended  with  extremely  serious  disad- 
vantages. In  the  first  place,  the  operation  of  laying  them 
down  is  an  exceedingly  dangerous  one,  especially  if  the  sea 
is  at  all  rough,  for  the  firing  arrangement  has  to  be  placed 
within  the  torpedo  before  it  is  moored,  and  as  soon  as  this 


ELECTRICITY  IN  WARFARE 


267 


is  done  it  is  liable  to  be  exploded  at  any  moment  by  an  acci- 
dental jar.  Another  serious  disadvantage  is  that,  unless  a 
secret  channel  is  left  open  for  the  passage  of  friendly  vessels, 
the  torpedoes  will  prevent  their  entrance  into  the  harbor 
just  as  much  as  hostile  ones;  and  if  such  a channel  is  left 
it  may  be  discovered  and  made  use  of  by  the  enemy.  Or 
again,  a friendly  vessel  entering  the  harbor  may,  through 
bad  weather  or  the  mistake  of  a pilot,  come  in  contact  with 
one  of  the  mines  and  be  destroyed.  Finally,  when  such  a 
system  of  mines  is  laid  down,  the  operation  of  taking  them 
up  when  no  longer  required  is  one  which  is  even  more 
dangerous  than  that  of  laying  them  down. 

All  these  defects  are  entirely  obviated  when  the  mines 
are  fired  by  means  of  electric  currents  which  can  be  con- 
trolled from  the  shore;  and  the  only  disadvantage  attending 
the  employment  of  the  latter  system  is  the  possibility  of  the 
enemy  obtaining  access  to  the  firing  station,  or  to  the  cables 
connecting  it  with  the  mines,  and  rendering  the  torpedoes 
harmless  by  cutting  the  cables. 

The  disadvantage  arising  from  this  possibility  is,  how- 
ever, a small  one  compared  with  those  attending  the  employ- 
ment of  purely  mechanical  submarine  mines,  and  there- 
fore those  now  employed  for  the  defence  of  harbors  and 
river  estuaries  are  almost  invariably  controlled  and  fired 
electrically. 

Electrically  controlled  torpedoes  may  be  divided  into 
two  classes — viz.,  those  which  are  fired  by  closing  the  circuit 
on  shore  when  a hostile  vessel  is  observed  to  be  sufficiently 
near  to  insure  the  explosion  taking  effect;  and,  secondly, 
electro -contact  torpedoes,  or  those  in  which  the  circuit  is 
closed  by  means  of  a circuit-closer,  either  contained  in  the 
torpedo  itself,  or  in  a small  buoyant  vessel  moored  to 


268 


ELECTRICITY  IN  MODERN  LIFE 


the  torpedo  by  a chain  or  cord  of  such  length  as  to  keep 
it  a short  distance  below  the  level  of  the  water. 

The  system  of  firing  by  observation  is  only  practicable 
in  clear  weather  and  by  day,  or  with  the  assistance  of  the 
electric  light,  while  the  electro-contact  system  can  be  em- 
ployed at  any  time.  On  the  other  hand,  the  electro-contact 
torpedo  will  only  explode  when  the  circuit-closer  is  actually 
struck  by  the  vessel,  and  as  torpedoes  have  to  be  moored 
at  a considerable  distance  apart,  in  order  that  the  explosion 
of  one  may  not  explode  its  neighbor,  the  explosion  of  one  of 
the  torpedoes  forming  a line  of  defence  would  necessarily 
greatly  reduce  the  chances  of  a ship  coming  into  collision 
with  an  electro-contact  mine,  though  it  might  easily  pass 
near  enough  to  be  destroyed,  or  at  any  rate  disabled,  by 
a submarine  mine  fired  by  observation.  Thus  the  most 
complete  safeguard  is  afforded  by  a combination  of  the  two 
systems. 

Submarine  mines  of  either  class  are  usually  charged 
either  with  some  form  of  dynamite  or  with  wet  guncotton, 
and  these  can  only  be  exploded  by  means  of  a bursting 
charge  formed  of  some  detonating  composition,  and  the 
most  suitable  material  for  this  purpose  has  been  found  to 
be  mercurial  fulminate.  The  fuse  is  usually  fired  by  the 
heating,  by  means  of  an  electric  current,  of  a fine  wire, 
usually  of  platinum,  or  an  alloy  of  platinum  with  silver  or 
iridium,  imbedded  in  a mixture  of  finely -powdered  gun- 
cotton and  mealed  gunpowder  in  equal  parts.  Below  this 
is  placed  the  bursting  charge  of  mercurial  fulminate.  Fig. 
89  shows  a fuse  of  this  kind,  which  is  employed  for  sub- 
marine mines  by  the  British  Government.  Fig.  90  shows 
a form  of  circuit-closer  suitable  for  electro-contact  torpe- 
does, designed  by  Colonel  Bucknill,  and  described  by  him 


ELECTRICITY  IN  WARFARE 


269 


in  a recent  volume  of  “Engineering,”  to  the  editor  of  which 
journal  I am  indebted  for  this  and  the  preceding  illustra- 
tion. MM  is  a permanent  horseshoe  magnet,  to  which  a 
ball,  B,  is  attached  by  means  of  a string,  as  shown  in  the 
diagram. 

If  the  buoy  containing  the  apparatus  is  struck  by  a vessel 
this  ball  is  drawn  sidewise  against  a silk  cord  connected 


'Multiple 

Capper 

Vitres 

covered 

with 

Cutta 

Pcrctia 


Plahnuim 
Silver 
Bnct^e  ■ 

faperor 

cSUco 

Oiaphrant 


f 


Binding 

Ebonite 

PeaCt. 

‘ Solid 
Copper 
Pillars. 
7 Platinum 
indium 
I'  Pndae 
iCidusI  q 
{Mealed 
[Powder 

hkrcurlQl 

fulminate 


Fig.  89. 


with  an  adjusting  screw  at  one  end,  and  with  a spring  detent 
at  the  other.  This  pulls  down  the  detent  and  releases  a 
wheel  driven  by  clockwork,  which  then  makes  a complete 
revolution  slowly,  during  which  period  the  cable  is  con- 
nected through  the  fuses  to  earth,  so  that  the  mine  can  be 
fired  if  desired.  The  effect  of  its  having  been  struck  is 
automatically  indicated  to  the  operators  on  shore,  and  the 


270 


ELECTRICITY  IN  MODERN  LIFE 


time  taken  by  the  rotation  of  the  wheel  gives  them  time 
to  discover  whether  the  circuit-closer  has  been  operated  by 
the  shock  of  a countermine  or  by  a blow  from  a hostile 
vessel. 

To  the  poles,  NS,  of  the  magnets  are  secured  the  cores 
of  two  low  resistance  electro-magnets,  CC,  one  end  of  the 
coil  wire  being  connected  with  the  line,  and  the  other  to  a 
contact-stud,  h.  The  armature.  A,  is  secured  by  a spring 
to  the  fixed  insulated  point,  P,  whence  an  insulated  wire  is 
carried  through  the  fuses  to  earth.  The  other  end  of  the 
armature  spring  carries  a contact-stud,  a,  which  engages 
with  h when  the  armature  is  attracted  to  ns^  the  poles  of  the 
electro-magnet,  to  which  it  is  prevented  from  permanently 
adhering  by  means  of  two  small  ivory  pegs  fixed  to  the 
under  side  of  the  cores.  The  strength  of  the  armature 
spring  can  be  adjusted  by  means  of  a second  spring,  Q. 
An  India-rubber  ring,  r,  tied  to  a metal  ring  prevents  the 
ball,  B,  from  oscillating  too  violently.  When  this  appa- 
ratus is  employed  as  a detached  circuit-closer  for  a large 
mine  moored  below  it,  the  stud,  5,  is  earth-connected  through 
an  interposed  resistance  of  about  1,000  ohms,  and  in  all  cases 
P is  connected  to  earth  through  the  fuses.  This  circuit- 
closer  can  be  used  either  for  firing  the  mine  by  observation 
or  by  contact. 

In  firing  by  observation  its  action  is  as  follows: 

The  coils,  CC,  are  wound  so  that  a negative  current  from 
the  shore  increases  the  normal  polarity  of  the  soft  iron  cores; 
consequently  when  the  negative  pole  of  a firing  battery  is 
connected  with  the  line,  a current  passes  through  the  coils, 
CC,  and  through  the  1,000  ohms  resistance  to  earth,  causing 
the  armature.  A,  to  be  attracted  to  the  electro-magnet,  and 
thereby  sending  a current  from  the  fuses  to  the  earth,  the 


ELECTRICITY  IN  WARFARE 


271 


resistance  on  the  fuse  circuit  being  low  enough  to  cause 
the  mine  to  be  exploded. 

If,  on  the  other  hand,  it  is  desired  to  fire  the  mirre  by 
contact,  the  negative  pole  of  a weak  but  constant  battery  is 
connected  to  the  line,  and  when  the  circuit-closer  is  struck, 
the  armature  is  held  up  mechanically,  and  retained  in  that 
position  by  the  magnetic  attraction.  The  signalling  battery 
gives  a signal  to  the  shore,  and  the  firing  current  can  now 
be  switched  into  the  line  or  not  as  desired,  the  mine  struck 
being  indicated  at  the  firing  station  by  the  deflection  of  a 
galvanometer,  and  by  causing  an  electric  bell  to  be  rung. 
Only  one  mine,  with  a detached  circuit-closer  arranged  in 
this  manner,  can  be  attached  to  the  same  line,  but  when 
the  apparatus  is  employed  for  mines  to  be  exploded  by  con- 
tact only  the  wire  from  b through  the  1,000  ohms  coil 
is  omitted,  and  several  mines  can  then  be  connected  with 
a single  cable,  either  one  after  the  other,  or  in  a bunch. 

Gun-Firing  by  Electricity. — Electrical  arrangements  are 
now  very  frequently  adopted  for  firing  all  the  guns  in  a 
battery  simultaneously,  or  for  firing  a broadside  from 
a man-of-war. 

In  the  latter  case  the  conducting  wires  are  carried  to  the 
conning -tower the  shot-proof  tower  from  which  the  captains 
of  our  modern  turret-ships  will  direct  the  evolutions  of  a 
vessel  during  a naval  engagement. 

When  the  vessel  is  approaching  an  enemy’s  ship  the 
gunners  will  keep  each  gun  trained  upon  the  enemy’s  vessel, 
and  the  captain  will  depress  the  button  at  the  moment  that 
he  considers  the  right  one  for  delivering  the  broadside. 
This  arrangement  will  probably  prove  to  be  of  the  utmost 
value,  as  there  is  little  doubt  that  in  the  next  naval  engage- 
ment the  first  effective  broadside  will  sink  or  totally  disable 


272 


ELECTRICITY  IN  MODERN  LIFE 


the  vessel  receiving  it,  so  that  the  result  of  a combat  between 
two  ironclads  will  mainly  depend  upon  which  vessel  is  able 
to  fire  first  with  effect. 

The  Telegraph  and  the  Telephone  in  T^ar.-r-The  establish- 
ment and  maintenance  of  an  effective  system  of  telegraphic 
communication  between  the  different  armies,  and  the  differ- 
ent portions  of  each  army,  engaged  in  a campaign,  has 
already  been  proved,  by  the  experience  of  several  great 
wars,  to  be  of  the  utmost  possible  importance;  and  in  addi- 
tion to  the  fixed  lines,  carried  upon  poles  or  underground, 
portable  lines  are  employed  to  a considerable  extent,  the 
line-wire  being  wound  upon  drums,  which  are  carried  on  to 
the  field  of  action,  so  that  the  commander-in-chief  can 
telegraphically  direct  the  operations  even  of  the  divisions 
actually  engaged  in  fighting. 

It  might  at  first  sight  appear  that  the  telephone  could  be 
employed  with  advantage  to  replace  the  ordinary  telegraphic 
signalling  instruments  for  such  a purpose  as  this,  but,  as  is 
pointed  out  by  Messrs.  Preece  and  Maier  in  their  work 
on  the  telephone,  its  use  under  such  circumstances  is  open 
to  very  serious  objections. 

In  the  first  place,  it  is  an  invariable  and  salutary  rule  in 
the  British  army  that  all  important  orders  must  be  delivered 
in  writing,  and  the  value  of  this  rule  is  shown  by  the  num- 
ber of  instances  on  record  in  which  fatal  blunders  have  been 
directly  traced  to  the  misapprehension  of  verbal  orders. 
Now,  as  is  pointed  out  in  the  work  alluded  to,  an  order 
transmitted  by  telephone  is  worse  than  a verbal  order 
delivered  from  one  person  to  another,  as  it  will  probably 
be  transmitted  verbally  between  two  clerks  who  do  not 
understand  its  meaning,  by  means  of  a mechanism  which, 
although  of  the  greatest  value  and  ingenuity,  is  far  less 


ELECTRICITY  IN  WARFARE 


273 


efficient  than  the  human  voice  addressed  directly  to  the  ear; 
and  in  illustration  of  this  an  incident  is  mentioned  which 
occurred  on  a military  line^  fortunately,  however,  in  time 
of  peace,  when  some  intelligence  as  to  the  whereabout  of 
a submarine  mine  case  at  the  Needles  was  received  as  an 
urgent  demand  for  a case  of  needles. 

If  such  mistakes  as  this  can  occur  in  time  of  peace,  there 
can  be  no  doubt  that  they  would  be  much  more  frequent  if 
the  telephone  were  employed  upon  the  battlefield,  where 
the  roar  of  cannon  and  the  rattle  of  musketry  would  be 
reproduced  by  the  transmitters  and  greatly  interfere  with 
the  distinctness  of  reproduction  of  a message. 

There  can  be  no  doubt,  however,  that  there  will  be  great 
scope  for  the  use  of  the  telephone  in  camps,  not  in  the 
immediate  presence  of  lUe  enemy,  for  carrying  out  the 
routine  business  of  the  camp,  promulgating  orders,  requisi- 
tions, etc.,  and  its  use  would  not  only  reduce  the  number  of 
orderlies  at  present  required  to  conduct  the  large  amount 
of  correspondence  of  this  kind  in  a large  camp,  but  would 
very  greatly  diminish  the  loss  of  time  between  the  asking  of 
a simple  question  and  the  receipt  of  the  answer.  The  tele- 
phone is  also  found  to  be  of  considerable  use  as  a telegraph 
receiver  for  employment  in  field  telegraph3q  as  it  is  exceed- 
ingly sensitive,  so  that  communication  can  be  carried  on 
through  faulty  lines,  or  even  through  bare  wires  simply  laid 
upon  the  ground.  This  sensitiveness  also  enables  much 
smaller  battery  power  to  be  employed  than  is  required  when 
ordinary  telegraph  receivers  are  used.  Another  very  great 
advantage  is  that  when  the  telephone  is  used  as  a telegraph 
receiver  it  never  requires  adjustment,  and  this  often  saves 
a considerable  amount  of  time  in  rapidly  running  out  a line 
and  establishing  communication. 


274 


ELECTRICITY  IN  MODERN  LIFE 


Messrs.  Preece  and  Maier  inform  us,  moreover,  that  the 
buzzing  signals  given  in  the  telephone  receiver  are  much 
more  easily  picked  up  by  signallers  trained  to  read  flag  and 
lamp  signals  than  those  of  the  Morse  instruments.  The 
current  used  is  an  intermittent  one,  and  this  intermittent 
current  produces  a musical  note  in  the  receiving  telephone. 

This  system  has  been  used  with  great  advantage  in  our 
recent  wars,  including  the  Egyptian  and  the  Bechuanaland 
expeditions. 

All  the  messages  from  the  field  of  Tel-el-Kebir  were  sent 
in  this  manner,  and  in  the  Nile  expedition  it  was  found  on 
several  occasions  that  its  use  enabled  very  important  mes- 
sages to  be  sent  through  portions  of  a long  line,  which, 
owing  to  faults,  were  unworkable  by  ordinary  instruments. 

The  telephone  is  used  to  a considerable  extent,  and  with 
the  greatest  advantage,  in  rifle  practice,  both  in  this  country 
and  in  Germany,  for  communicating  between  the  markers 
at  the  target  and  the  firing  station. 


MEDICAL  ELECTRICITY 


276 


CHAPTER  XIX 

MEDICAL  ELECTRICITY 

The  electrical  phenomena  presented  by  the  tissues  of 
the  living  animal  body,  obscure  as  the  subject  is, 
deserve  a brief  mention;  especially  as  electricity 
is  now  so  largely  used  in  the  treatment  of  various  diseased 
conditions. 

Muscle  and  nerve  are  the  living  tissues  par  excellence, 
and  it  is  their  changes  of  electrical  state  which  have  been 
most  studied. 

Currents  of  Rest. — If  one  end  of  a cylindrical  muscle  is 


cut  off,  as  shown  in  the  diagram,  Eig.  91,  and  one  electrode 
of  a galvanometer  of  appropriate  construction  placed  on  the 
centre  of  the  cut  surface  at  A,  while  the  other  electrode 
placed  on  the  equator  of  the  muscle,  BB,  the  existence 
an  electric  current  between  the  two  points  will  at  once 
clearly  evident.  The  existence  of  a similar  current  in  a 


S'  a s* 


276 


ELECTRICITY  IN  MODERN  LIFE 


piece  of  a nerve-trunk  similarly  treated  can  be  demonstrated 
in  the  same  manner,  though  the  nerve  current  is  much 
feebler  than  the  muscle  one.  These  currents  are  termed 
“Currents  of  Eest”;  but  whether  they  are  natural  or  arti- 
ficial— i.e.,  whether  existent  in  perfectly  healthy  tissues, 
or  only  as  a result  of  injury — is  a question  which  is  still 
suhjudice.  Those  who  maintain  the  latter  view  lay  stress 
on  the  undoubted  fact  that  the  surface  of  the  quiescent  frog’s 
heart,  which  is  practically  a mass  of  muscle,  is  iso-electric — 
i.e.,  on  whatever  two  points  on  its  surface  the  electrodes  are 
placed  no  current  flows  through  the  galvanometer. 

Currents  of  Action, — Whatever  be  the  truth  as  regards 
the  currents  of  rest,  there  is  no  question  as  to  the  occurrence 
of  marked  changes  of  electrical  condition  when  a muscle  or 
a nerve  is  stimulated.  If,  in  a muscle  prepared  as  above, 
the  galvanometer  is  showing  a distinct  current  of  rest,  as 
soon  as  the  muscle  is  made  to  contract  by  stimulating  its 
nerve,  the  needle  of  the  galvanometer  swings  back  toward 
zero,  a phenomenon  known  as  the  negative  variation  of  the 
current  of  rest.  But  a like  electrical  change  can  be  demon- 
strated even  In  the  absence  of  any  current  of  rest — e.g.,,  at 
each  contraction  of  a frog’s  heart  a very  distinct  current 
shows  itself.  Hence  the  term  “Current  of  Action”  is  pre- 
ferred by  those  who  deny  the  existence  of  any  natural 
•‘Current  of  Rest.”  This  change  of  electrical  state  in  the 
muscle  precedes  the  change  of  form  which  is  the  visible 
result  of  stimulation,  and,  like  the  contraction,  travels  in 
the  form  of  a wave,  each  portion  of  muscular  substance, 
as  it  contracts,  becoming  negative  to  those  portions  which 
have  not  yet  contracted,  or  which  have  returned  to  a state 
of  rest. 

A similar  wave  of  change  of  electrical  state  traverses  a 


MEDICAL  ELECTRICITY 


277 


nerve  which  has  been  stimulated;  it  travels  at  the  same  rate 
as  the  nervous  impulse,  about  twenty-eight  metres  per 
second  in  a frog’s  nerve — a rate  so  much  slower  than  that 
of  an  ordinary  electric  current,  that  by  itself  it  suffices  to 
show  that  the  nervous  impulse  is  something  essentially 
different  from  an  electric  current.  The  association  of  such 
electrical  changes  with  vital  phenomena,  when  first  observed, 
led  some  too  hasty  people  to  the  conclusion  that  they  were 
identical,  a view  to  which  are  due  the  foolish  statements, 
e.g.,  “Electricity  is  Life,”  which  figure  so  prominently  in 
the  advertisements  of  various  quacks. 

The  use  of  electricity  for  medical  purposes  depends 
largely  on  the  fact  that  the  activity  of  the  muscles,  nerves, 
and  other  tissues,  normally  dependent  on  that  of  the  central 
nervous  system — i.e.^  the  brain  and  the  spinal  cord — can, 
nevertheless,  be  evoked  by  other  means,  mechanical,  chem- 
ical, thermal,  or  electrical.  The  following  facts  illustrate 
the  nature  of  the  influence  exerted  by  electricity  upon  the 
nerves  and  muscles. 

When  a continuous  current  is  passed  into  a nerve  at- 
tached to  a muscle,  a single  contraction  of  the  muscle  takes 
place,  and  a similar  contraction  occurs  when  the  current 
is  cut  off;  but  so  long  as  the  current  is  traversing  the  nerve 
the  muscle  remains  quiescent.  Although,  however,  there 
is  no  visible  change  in  the  nerve-muscle  preparation,  the 
condition  of  the  piece  of  nerve  traversed  by  the  current  is 
profoundly  modified ; it  is  in  a condition  known  as  electro- 
tonus,  and  it  can  readily  be  demonstrated  that  in  the  vicinity 
of  one  electrode  its  excitability  is  markedly  increased,  while 
in  the  vicinity  of  the  other  it  is  correspondingly  decreased. 
The  passage  of  an  intermittent  current,  consisting  as  it  does 
of  a rapid  success  of  shocks,  into  the  nerve  of  a nerve- 


273 


ELECTRICITY  IN  MODERN  LIFE 


muscle  preparation,  throws  the  muscle  into  a state  of  con- 
traction which  persists  as  long  as  the  current  is  passing, 
or  until  the  muscle  is  exhausted.  The  muscle  may  also 
be  made  to  contract  by  the  direct  application  of  an  electric 
current,  continuous  or  intermittent,  to  its  substance,  without 
the  intervention  of  the  nerve;  muscle  substance  is,  however, 
much  more  sluggish  in  its  response  to  an  electrical  stimulus 
than  is  nerve  substance,  and  unless  the  stimulus  acts  during 
an  appreciable  period  the  muscle  fails  to  respond.  Hence 
if  the  minute  nerve  filaments  which  ramify  through  a muscle 
be  destroyed  by  disease  or  paralyzed  by  drugs,  the  muscle 
cannot  be  made  to  contract  by  the  intermittent  current, 
whereas  the  continuous  current  affects  it  readily. 

Electricity  is  employed  by  physicians  both  for  diagnostic 
and  for  therapeutic  purposes.  As  a diagnostic  agent  its 
chief  use  is  in  cases  of  paralysis,  to  aid  in  deciding  the 
important  question  as  to  the  site  of  the  morbid  process,  or 
fault,  to  use  a telegraphic  term,  which  has  deprived  the 
brain  of  its  power  over  a muscle  or  group  of  muscles.  The 
lesion  may  be  in  the  central  nervous  system  itself,  or  any- 
where along  the  tract  of  communication  between  this  and 
the  muscle  or  muscles  affected — i.e.,  it  may  be  central  or 
peripheral.  In  the  latter  case  the  minute  nerve  filaments, 
which  ramify  through  the  muscle  substance,  waste  away,  so 
that  the  muscle  can  no  longer  be  made  to  contract  through 
their  agency;  in  such  a case  the  muscle  makes  no  response 
when  stimulated  by  the  intermittent  current,  whereas  its 
reaction  to  the  continuous  current  is  even  more  prompt  than 
usual.  There  are  other  distinctions,  qualitative  and  quan- 
titative, on  which  it  is  unnecessary  here  to  dilate. 

The  therapeutic  uses  of  electricity  are  manifold.  One 
of  the  most  important  results  from  its  power  of  stimulating 


MEDICAL  ELECTRICITY 


279 


muscles  into  action.  When  the  communication  between  a 
muscle  and  the  central  nervous  system  is  impaired  by  dis- 
ease, the  muscle,  being  unused,  rapidly  wastes  away,  and  in 
cases  which  tend  to  recover  there  may  be  little  muscle  tissue 
left  by  the  time  that  the  natural  process  of  repair  has  re- 
stored the  integrity  of  the  affected  communication,  so  that 
the  paralysis  is  permanent.  In  such  cases  the  physician  is 
able,  by  the  aid  of  electricity,  to  give  the  paralyzed  muscles 
such  regular  exercise  as  suffices  to  keep  them  healthy  until 
the  central  nervous  system  has  had  time  to  regain  its  power 
over  them. 

Electricity  is  often  of  great  use  also  in  cases  of  neuralgia, 
rheumatism,  painful  spasm,  etc.  Thus,  a nerve-trunk  may 
be  in  an  unduly  excitable  condition,  or  may  be  conveying 
to  the  brain  impulses  originating  in  a disordered  peripheral 
organ;  by  putting  such  a nerve  into  the  electrotonic  condi- 
tion, its  excitability  or  conductivity  may  be  modified  in 
such  a manner  as  to  stop  the  passage  of  such  morbid  im- 
pulses, so  relieving  pain.  It  is  easy  to  see,  however,  that 
in  such  cases  the  character  and  direction  of  the  current  to 
be  employed  are  points  requiring  careful  consideration;  and 
if  used  without  knowledge  the  remedial  agent  may  aggra- 
vate instead  of  alleviating  the  morbid  condition. 

Electricity  is  also  frequently  employed  for  its  chemical 
and  thermal  effects.  Electrolysis  may  be  set  up  in  a tumor, 
so  initiating  processes  which  stop  its  growth,  or  cause  its 
gradual  destruction;  or  in  an  aneurism,  to  cause  coagulation 
of  the  blood  and  consequent  consolidation  of  the  aneurism. 
For  cauterizing  purposes,  also,  in  parts  of  the  body  difficult 
of  access,  the  electric  current  is  frequently  employed  to  heat 
a wire  previously  placed  in  situ. 

As  an  illuminating  agent  electricity  is  frequently  em- 


280 


ELECTRICITY  IN  MODERN  LIFE 


ployed  to  examine  various  passages  and  hollow  organs 
of  the  body,  the  pharynx,  stomach,  bladder,  urethra,  etc. 

In  conclusion,  it  may  be  well  to  remark  that  electricity 
is  not  a universal  panacea,  and  that  it  does  not  act  like  a 
magical  incantation.  When  the  effect  to  be  obtained  is 
clearly  realized,  and  the  means  employed  are  adequate  and 
appropriate,  the  use  of  electricity  will  often  be  of  the  great- 
est benefit;  in-  the  absence  of  these  conditions  it  is  far  more 
likely  to  be  harmful.  It  is  only  fair  to  observe  that  the 
majority  of  the  people  who  vaunt  their  marvellous  belts 
and  other  electrical  appliances  appear  to  have  borne  this 
fact  in  mind,  and  avoid  harming  their  patrons  by  supplying 
apparatus  which  is  as  innocuous  as  it  is  useless. 


APPLICATIONS  OF  ELECTRICITY 


281 


CHAPTER  XX 

MISCELLANEOUS  APPLICATIONS  OF  ELECTRICITY 

IT  WOULD  be  impossible  in  the  space  at  my  command 
to  enumerate  all  the  various  useful  purposes  to  which 
electricity  is  now  applied,  but  I have  thought  it  well 
to  devote  a short  chapter  to  a few  interesting  applica- 
tions of  electricity  which  could  not  suitably  be  included 
in  any  of  the  preceding  ones. 

A very  interesting  and  useful  application  of  electricity 
in  private  houses  is  one  whiph  is  now  extensively  adopted 
in  America  for  enabling  private  dwelling-houses  to  be  shut 
up  during  the  absence  of  their  owners  without  danger  of 
being  broken  into  by  thieves,  thus  doing  away  with  the 
necessity  of  employing  caretakers. 

The  system  is  a very  simple  one,  and  consists  in  carrying 
a continuous  wire  in  front  of  every  door  and  window  in  the 
house,  in  such  a manner  that  none  of  them  can  be  opened 
without  breaking  or  cutting  the  wire.  One  end  of  the  wire 
is  put  to  earth,  while  the  other  is  carried  to  the  central  sta- 
tion established  by  the  company  working  the  system,  and 
connected  to  one  of  the  terminals  of  a galvanometer,  the 
other  terminal  of  which  is  put  to  earth.  An  electric  current 
is  kept  continuously  flowing  through  each  of  the  circuits 
thus  meeting  at  the  central  station,  either  by  inserting 
batteries  in  the  circuit,  or  by  means  of  a dynamo  at  the 


282 


ELECTRICITY  IN  MODERN  LIFE 


central  station.  The  galvanometers  are  watched  day  and 
night,  and  if  any  one  of  the  circuits  is  broken  the  fact  is 
at  once  indicated  to  the  watchman  by  the  needle  of  the 
galvanometer  going  to  zero.  When  this  happens  the  police 
are  immediately  communicated  with,  and  a man  is  at  the 
same  time  sent  round  from  the  central  station  to  repair 

the  breakage  and  to  find  out 
whether  the  interruption  was  due 
to  accident  or  not. 

Soon  after  the  introduction 
of  this  system  into  the  city  of 
Washington  a negro  attempted 
to  effect  an  entrance  into  a house 
protected  in  this  manner.  He 
was  aware  that  the  house  was 
protected  in  some  mysterious  way 
by  means  of  a wire  carrying  an 
electric  current,  and  thinking  to 
make  quite  sure  of  obviating  any 
disagreeable  effects  to  himself,  he 
took  the  precaution  of  cutting  the 
wire,  and  then  watched  for  a con- 
siderable time  to  see  what  would 
happen.  As  he  was  unable  to  perceive  any  effect  as  the 
result  of  his  action,  he  then  effected  an  entry  into  the  house. 
The  police,  however,  had  been  communicated  with,  and  had 
been  watching  the  burglar  the  whole  time,  so  that  he  was 
immediately  followed,  handcuffed,  and  removed  to  the  police 
cells,  much  to  his  disgust  and  astonishment. 

Electric  bells  are  now  in  very  general  use  in  this  coun- 
try, as  well  as  in  America,  and  they  seem  almost  too  well 
known  to  need  description,  but  perhaps  a brief  account 


Fig.  92. 


APPLICATIONS  OF  ELECTRICITY 


288 


of  their  construction  and  manner  of  working  may  not  be 
without  interest. 

The  ordinary  form  of  electric  bell,  with  its  cover 
removed,  is  shown  in  Fig.  92.  It  consists  of  an  electro- 
magnet in  circuit  with  a 
battery,  the  circuit  re- 
maining open  when  the 
bell  is  not  in  use,  and 
being  closed  by  some 
form  of  push-button. 

When  the  circuit  is 
closed,  the  armature  of 
the  electro-magnet  is  at- 
tracted by  the  iron  core 
within  the  coils,  and  the 
hammer  attached  to  it 
strikes  the  bell.  When 
the  armature  is  thus 
drawn  toward  the  electro- 
magnet, the  circuit  is 
broken,  the  electro-mag- 
net  becomes  demagne- 
tized, and  the  armature 
springs  back  to  its  orig- 
inal position,  and  again 
completes  the  circuit  through  the  contact  point  shown  in  the 
diagram.  As  long  as  the  push-button  is  kept  pressed  down 
the  bell  will  continue  ringing. 

This  is  the  system  generally  employed  in  private  houses, 
but  in  hotels  an  indicator  is  usually  attached  to  each  bell, 
and  when  the  push-button  is  depressed,  not  only  does  the 
bell  ring,  but  the  indicator  falls,  and,  as  iong  as  it  is  down. 


284 


ELECTRICITY  IN  MODERN  LIFE 


completes  the  circuit  without  the  intervention  of  the  button, 
so  that  the  bell  continues  ringing  until  the  servant  whose 
business  it  is  to  answer  it  has  replaced  the  indicator,  thus 
insuring  that  the  call  should  not  pass  unnoticed.  The  indi- 
cators belonging  to  all  the  rooms  in  a hotel  are  usually 
arranged  upon  a single  board  in  the  manner  shown  in 
Fig.  93. 

Many  shops  and  warehouses  are  now  provided  with  elec- 
tric alarms,  which  set  a bell  ringing  if  the  temperature  rises 
to  such  an  extent  as  to  indicate  that  a fire  has  broken  out, 
or,  if  no  one  is  living  on  the  premises,  a signal  is  auto- 
matically sent  to  the  nearest  fire  station.  Similar  alarms 
are  now  employed  in  greenhouses  to  ring  a bell  in  the 
gardener’s  cottage  when  the  temperature  rises  above  or  falls 
below  certain  limits. 

All  the  clocks  in  a large  establishment  can  be  regulated, 
if  desired,  by  means  of  electric  currents,  from  one  central 
one,  so  that  it  is  sufficient  to  have  one  first-rate  clock  in  the 
system,  the  others,  of  inexpensive  construction,  being  made 
to  keep  exact  time  by  the  central  regulator. 

Another  application  of  electricity  of  quite  recent  dis- 
covery, but  which  promises  to  be  of  considerable  impor- 
tance, consists  in  its  employment  for  decomposing  the 
offensive  gases  in  our  sewers,  and  removing  the  poisonous 
properties  of  their  fluid  contents,  so  that  after  such  treat- 
ment they  may  be  allowed  to  discharge  into  rivers  without 
fear  of  spreading  diseases. 

The  employment  of  electric  currents  for  exploding  sub- 
marine mines  would  naturally  suggest  the  advantage  of 
using  electricity  in  the  same  manner  for  exploding  blasting 
charges  in  mining  operations,  and,  as  a matter  of  fact,  it  is 
now  employed  to  a considerable  extent  for  this  purpose. 


APPLICATIONS  OF  ELECTRICITY 


285 


A very  striking  example  of  its  advantages  was  given 
in  the  blowing  up  of  the  rocks  at  Hell  Grate  in  New  York 
Harbor  some  years  ago,  when  a mass  of  many  thousand  tons 
of  rock  was  blown  up  by  means  of  dynamite  cartridges  in- 
serted in  channels  which  had  previously  been  bored  by 
divers  in  all  directions  through  the  rock,  and  which  were 
exploded  simultaneously  by  the  passage  of  an  electric 
current. 

One  more  application  of  electricity  I must  mention,  but 
only  to  deprecate  it,  and  that  is  the  proposal  to  employ  it  for 
the  execution  of  criminals,  which  has  been  recently  made 
in  the  United  States. 

Every  one  who  has  any  competent  knowledge  of  the  sub- 
ject knows  that  the  greatest  possible  uncertainty  attaches 
to  the  effects  of  electric  discharges  upon  human  and  other 
animal  life,  and  though  there  would  be  no  difficulty  in 
employing  a current  of  sufficient  ‘strength  to  insure  imme- 
diate death,  this  result  could  only  be  attained  with  absolute 
certainty  by  the  use  of  currents  which  would  terribly  dis- 
figure the  body  of  the  criminal,  and  the  legislature  of  the 
State  of  New  York  has  expressly  stipulated  that  the  currents 
must  not  be  such  as  would  cause  disfigurement. 

I have  no  hesitation,  therefore,  in  maintaining  that  it 
would  be  a most  retrograde  step  to  replace  the  present 
simple  and  humane  method  of  terminating  a criminal’s 
existence  by  one  which  in  some  cases  might  allow  him  to 
escape  with  impunity,  and  in  others  might  subject  him  to 
horrible  tortures  before  life  became  extinct. 


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UNIVERSITY  OF  ILLINOIS-URBANA 


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